I know but if you pay them with your card it might be linked to you, as we saw what happened with proton

Make sure to buy it through a proxy, like f.e. https://digitalgoods.proxysto.re/en . That way they will never be able to link it to you.

Yes it does ( did it like 5 weeks ago)

Never had a website or service deny an email change in my 25 years of being on the internet. But you can move all the other stuff to a different email and keep the ones you can’t change on your gmail. Still a better choice than giving all your data to google.

No alternative? Immich and Ente are definitely an alternative Google Photos. It ain’t that hard to degoogle these days.