It appears that proton’s is only for them and they don’t offer it to other websites unfortunately

https://proton.me/blog/proton-captcha

Your ISP can see that you used tor but not what for

If you’re worried about notifying the sender that you are a real person, it’s probably not great interacting with the links at all because they are linked directly to your email (same with normal unsubscribe links)

They also support payment in Monero so you don’t even need your crypto chain

Either way the Matrix homeserver you’re connecting to will log your IP