It was a many months transition, and it's finally done
Fun thing, you can actually make a backup of all* your messages, groups, contacts, etc. So before leaving you can have all of your data in case you need that one contact or something
The final red flag was as that allegedly Russian authorities were messing with people's deleted messages. Not for the first time there are news that they could read, modify, delete, see location, and etc. Screw it, this is unsafe, I'm out.
Also, these days telegram is really at the state of a pile of garbage, bloated, buggy, and shady messenger.
FYI, regular Signal now has usernames available with the option to hide your phone number switched on by default (you may still need tithe beta release for the next few months since it's staggered rollout)
Signal still requires a SIM card & an Android or iOS primary device. Usernames here just let you cloak your phone number, not keep it a secret from the service.