May I ask your personal experience ? - Would it be useful to showcase your master's work to look for a job, for example?

I thought universities usually put the thesis's of Masters students by research online. Though I may be wrong. It is nice for it to be online but I doubt many people will read it.

I've heard some German universities do that. But it seems that UK, US & French unis don't save master's dissertations online.
My master's dissertation isn't online :( Apparently my uni (in the UK) can't be arsed to do it.
I think it's good to put it online if you think your master's research is of high quality. If you're unsure, just ask your supervisor. If your supervisor says it's better not to put it online because the research quality isn't high, then don't do it.

It's a given continental thing; it's just how the system works. In the UK it's the opposite; it's rare for them to be published and I generally counsel students to consider it carefully if approached as publishers will sometimes opportunistically raid your wallet in an elaborate vanity scam.

Considering you have a copy yourself and can submit it or link to it on an application that's what I'd recommend. If you think it's useful and could be cited, then ResearchGate etc. would provide you with a means for making it accessible. Few (no) employers will actually read it in full, but the majority will (hopefully) dip in if it's available, and if it showcases your ability to write and present research it's a good thing to have, but not a deal-breaker.