By the way, let me say a bit more about myself. My PhD research is a cross between biology, chemistry, and physics. I collected lots of data during my PhD, but then I didn't have any first author papers. My supervisor used my data to complement other group members' data, and other group members are always the first author and I'm the second. I'm definitely unhappy and have protested, but that's no use. My supervisor just didn't listen. No matter how hard I tried, my supervisor just ignored what I said and chose to do whatever he wanted to do. So it ended up I'm always the second author. I don't know how much impact this had made on my postdoc applications, but I think those PIs wouldn't let me know this. Also, when I told my supervisor I started to apply for postdoc positions and asked him to prepare a reference letter for me in June, he didn't say anything. Rather, he looked unhappy. Later, those PIs who requested ref letters received the letter from my supervisor, so that means he wrote the letter. But I've no idea what he wrote about in the letter. Maybe he wrote something negative? Anyway, I don't know how I can lower the impact made by having no first author papers...And I don't know how I can see what my supervisor wrote in the ref letter. Maybe I can never see it.

I haven't submitted my thesis yet, so I'm also feeling stressed about the thesis. Maybe this is not the best time to think about postdoc positions, but I can't help it.

I've been looking for a postdoc position for 6 months. I started to do it last June, and in July when I got two rejections, I thought I would try again and again and would give myself 6 months to find one. I planned to quit and do something else if I still hadn't found a position in 6 months. Now, however, 6 months passed, but I still don't want to quit. It's been a long time and been exhausting. It took lots of time to search for information, contact the PIs who posted the ads, make applications, and prepare for interviews. It took so much time that it has made my thesis writing much slower. But all the efforts are futile. All the time is forever lost, and I got nothing. No offers at all. And I have to catch up with my writing.
I don't know if I should continue to do so. I'm so drained.

They always tell me my expertise is not directly related to their projects. They always tell me someone else is more suitable for their position. I'm so tired of this. When I finally saw an ad for a position that was directly related to my PhD research, I thought I would no longer be told I was not suitable enough, and I thought I would be given an interview and would receive an offer soon afterwards. I applied. But then I received a rejection without an interview. I was so surprised that I contacted the PI and asked him why. He just said I wasn't experienced enough. So I thought the best candidate must be a postdoc who has more experience than me in this field. But it turned out the person who was offered the position was also a final year PhD student, who's even less experienced than me (her PhD research was not directly related to this project, but mine was). I was shocked. I again contacted the PI and asked why. He didn't reply. I'm so disappointed. I really don't know how PIs choose their best candidates and the real reason why each of them rejected my application.

If an international student is thinking about doing a STEM PhD, I will definitely tell them not to do so. When you're doing a STEM PhD, you're working for your supervisor, and you're supposed to be paid by your supervisor.
But it seems that you're doing politics. In politics, it seems that PhD students are working for themselves. So it may be worth it if you go self-funded. You'd better consult PhD students in your field before you make a decision.

In the UK, once you start to do a PhD, you can hardly get any funding. If you need funding, you need to secure a funding before you start your PhD.

I'm a female student, and I find physical contact with my male supervisor uncomfortable.
Are there any other female PhD student here whose male supervisor touches your body from time to time? Can you let me know how you feel about it? Do you think your supervisor is just being friendly?
When I'm having meetings with him, he tapped me on my arm, thigh, back, or hand from time to time. It's not frequent, and it doesn't happen at every meeting. But it makes me uncomfortable. Am I oversensitive? Should I tell him I'm not comfortable with that? It's so embarrassing to tell him about that. Maybe he will get angry and that will jeopardize our working relationship. I'm a bit scared.
One day I even noticed that he stared at my bum. The way he looked at my bum really scared me. But I was too embarrassed to ask him about it.
I'm not really sure if it's sexual harassment. And I don't have the courage to ask my group members. They are all male, so I don't think they will understand my feelings. I feel I'm not respected by my supervisor. But if I ask my male lab mates, I'm sure they will laugh it off and tell me I'm too sensitive. And everyone in this group, including me, knows that our supervisor is a happily married man, who has a very good-looking wife (yes she looks like a super model!). Obviously he has no motives for sexually harassing a plain-looking student.

People told me I should reach out to potential postdoc supervisors about 6-12 months before I finish my PhD and stay in touch with them.

But what should I say when I email them? Should I just ask them if they plan to take on a new postdoc this year? But they don't have an ad for the recruitment, which clearly shows that they don't have any money at the moment for a new postdoc (if they had the money, then they would post an ad for sure!). So asking if they are recruiting a postdoc sounds like a stupid question. And if they do have an ad, then I should just submit an application - what's the point in reaching out to them before I submit an application?

And what other things can I say in my emails to them? Maybe I should introduce myself? But if they don't have money for a new postdoc, it should be meaningless to introduce myself I think?

I really don't understand why people keep telling to start early and reach out to the academics I'm interested in. I don't think I have anything to say to them.

I think you need to get out of this shithole as soon as possible! This PI tricked you, and later they will probably continue to do harm to you. The sooner you get out of there, the better you will protect yourself from further harm.
And you don't need to hide anything from any potential PI when you look for a new position. It's not your fault, so just tell them the truth. Once you tell them the true reason behind your move, they'll see you're a true scientist and an ambitious young researcher.

This professor didn't give you any details, but if you're curious you can ask them for clarification.
This pandemic is really annoying and has fucked up the whole academia. I've heard many universities in the UK, US, and Australia have laid off some teaching staff and researchers. Many US universities have stopped recruiting new tenure-track academics. The main reason is lack of money. I guess your situation also has something to do with money.

I'm mainly asking about the situation in the UK. But if you're in another country, you can also talk about the situation in your area.
From June, many labs in universities have reopened. But recently, many areas have gone into local lockdown. I'd like to learn how the new lockdowns have affected your lab work.

I haven't been on here for a long time. If OP is still here, I just want to say, hey, OP, you're not alone!
I've seen so many things like this. Many supervisors are biased. So are departmental heads. When things happen, their bias make them choose to take one side, and treat the other side like rubbish. And when you ask for clarifications, they will never give you any clarifications. When they're biased, they are biased. They wouldn't admit it. They never acknowledge they've done anything wrong. They have power over you and they could do anything they want. You just can't get any justice from them. If you resist, they will take it further and make more people go against you. They're just like that. That's the true face of academia. I've never seen a PhD student who successfully resists the evilness from the people who have power.
If you want to get the university involved, you could try, but don't expect too much. The involvement of the university will be time-consuming and take away lots of energy from you. Lower your expectation. Also, try and talk to the potential university and see if that university can help.