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.
I mean from what I gather e2ee is not on by default (and unsuppoeted in group) and is proprietary.
The link below talks about why that is; Telegram focuses on features over maximize privacy.
https://www.wired.co.uk/article/telegram-encryption-end-to-end-features