Let me share something @didek pointed me at:
Should you want to #register at #telegram or want to change your phone number (basically everything that requires a #sms or #call sent to you):
It only works on a device with an official #telegram #build and with #google #playservices installed.
All other settings, e.g. vanilla #lineageos , #telegramfoss and other things fail silently or with misleading errors.
Did cost me 3 days to find out.