

Thank you for the detailed answer and overview of the different options! To clarify about Signal: in order to confirm a new account, Signal sends an SMS with a code to the registered number. In Russia, you cannot receive those messages since maybe 2 years ago. So all existing users are fine, but the new users can’t register an account.
Edit: typos
Wow,.lots of detailed information! Looks very helpful. Thank you, I bookmarked it and will read this weekend.