[miki123211]

How do they handle message recovery when all your devices have been lost (and possibly when you've forgotten your password)?

That's (almost) incompatible with E2E encryption. You could do it via "social proof" or server-side secure enclaves and pins, but that's about it.

[nullc]

Who cares? this stuff is all ephemeral messaging. People frequently don't have and can't find them if they do, even absent any security.

[GoblinSlayer]

Maybe in google profile backup, where all your data is stored.