Things are not great in academia when it comes to funding. If a PI has fund, he/she is "more likely" to post a job ad. Some PIs have some "hidden" funds or they have money from department which is not assigned to a particular project. You might try though the chance is not particularly high.
One expected reply is that PI asks you for a proposal either his/her proposal and you want you to work on it or your own proposal. Many academics think now that the Postdoc and even PhD students should bring their money with them.
Another important option is to seek fund from funding bodies that are willing to fund early stage researchers. The PI can guide you which funding bodies you can contact or you might start googling it before contacting PIs.

I understand well how you feel. You want to prove it to yourself not to anyone else. Being biased against "managment", I would recommend the finance and accounting Master. It looks like you love the subjects more and the chance that you will do well is higher if you have the passion. Moreover managmement career is comlicated and depends on many things the least of them is education in management.
But are you going to leave your job or work parttime? Are you ready for this massive change? I am not scaring you as I did several massive changes and did not regret them but just be prepared for the big change.

I think it is common in Postdoc. You work in a "closer" field where the fund is available. If you like the other field, it should be absolutely fine.

It is not easy with lower marks. I suggest you search for an RA job and try to publish then you will have a better chance. The other option is like PhoenixFortune said to do another Master. You can try with your current profile but it will be difficult.

There is no such a programme which is meant for graduates with non technical background. Just explore the programmes and apply with a good cover letter and I am sure you will be accepted at one of them.

Knowing what to do after PhD is not that critical as it looks. What would be wrong is to start a PhD because you have nothing else to do.
But if you love science, doing a PhD might be a good choice. You do not have to choose a "perfectly" matching subject. If you want to stay in a certain geographical location, a bit of compromise is expected. You do not have to choose between career and life style. You can sacrifice half of each. For example, some commute (one to two hours) with a job or PhD which satisfies you 60-80% would be nice. After Corona, commute will be the new normal as allowing employees to have a considerable time working from home would be not unusual.
One pro for PhD is that if you complete a PhD, you will have a chance to work in research institution or in a company that does some decent work utilising your education and knowledge. It is still possible with a Bachelor but with PhD the chances are higher.

I think you can just try to forget about him and apply everywhere. If I were you, I won't put this institution as a top priority.

I am sorry to hear this. You supervisor is not God and he does not control the universe. Even if you do not believe in God, he/she is a just a person. You do not need to apply at the same institution. But if you want to go to the same institution, just apply.
Just for curiosity, is you supervisor a woman? It has occurred to me that the worst manager/employee supervisor/student relationships are woman/woman. It turns often to personal which is a double-edged sword.

Hi. I agree with EM89. Focus to get things done. Major corrections is not a bad outcome. Also too much escalating can lead to worse outcome.

You can ask further questions but based on my experience, he will never reply. This is the final reply and he will not (and he does not have to) explain more. It is sad but it is what it is. Fund or pandemic it does not matter. Just move on and apply somewhere else. Meanwhile in a few months try to reach him out asking if the situation changes, although it is quite rare to reconsider applicants after rejection.

Hi. I do not think it goes this way. You do not have to know someone in Germany to get the visa. You have to show available funds in a Germany "blocked" bank account. Please check the following link
https://www.auswaertiges-amt.de/en/einreiseundaufenthalt/02-lernen-und-arbeiten/sperrkonto-seite

Although they might seem pretty similar, but I usually prefer the standard degree over "non standard" degrees. I do not like it when I have to explain my degree if it is not standard. Also the standard PhD gives you mobility outside the UK also if you want to shift the field a bit.

I agree with em, pm, and rewt. I would add that I were you, I separate two questions:
1. Do I want to continue? what is the point of completion, what am going to do after finishing?
2. Can I really finish?
If the answer to question 2, is really no and you need to "repeat" your PhD in one way or another, I would advise quitting. But if what you have done is satisfactory in terms of data collections and analysis, I would consider writing what I have already and try to finish it whatever comes next. It took me five years thinking of quitting and eventually fund ran out and left without PhD. You are not alone. No need to regret anything but think carefully.