Well that's that then. I also have no idea what to try anymore... I guess you'll just have to wait until some random update fixes the issue. Sorry.
Edit: Since you reinstalled everything, I think it could be some cache on your system that went bad. That would explain why both the Flatpak and native versions don't work and why the rest of your system works. But I have no idea where that cache might be...
While that would probably work, as I already said, I do not want to pay for one. It's less about the money but more about that I'd have to give them all my information - my name, credit card details and so on. And I am not willing to do that, as a VPN is only private until the government or whoever asks for all your data, which would include the Website and the fact that I visited it.