The seat is not what closes a toilet. That’s the lid and it’s not even mentioned on the sign.

Is there a way to automatically add books to it when a book in my Calibre Library gets marked as completed?

https://keyboard.futo.org/ is a good one!

Uh, never heard of it! Looks very promising. Are third party clients officially allowed by Signal?

As far as I know they added usernames which you use to identify people. But to sign up you still need a phone number to verify through a code they send you.

All I want is anonymous sign-up.

Maybe you can find something here: https://archive.org/details/wikimediadownloads