In the April 2021 Newsletter I have read that Squirrelmail is going away. I don't know if I'm using Squirrelmail or Roundcube... How should I change my mail options? If don't change it, am I going to loose my email address?
https://mail.riseup.net is Roundcube. It's the default mail interface, and has been for a long while.
To log into squirelmail, you'd have to use this link: https://sm.riseup.net/sm/src/login.php
So you probably use Roundcube :)