You’re welcome. Since that’s how installing “unknown apps” works in Android, I thought it might work similarly in a de-googled phone.
On my Android phone, I removed my Telegram Android app from the Google Play store and replaced it with the downloaded Telegram Android app directly from the Telegram website, Telegram for Android. My Android phone made me turn on permission to install unknown apps in order to do that, and keep that permission enabled so I could receive the updates from Telegram.
Now, when I’m working in Telegram’s Android app, I’ll be notified within Telegram that an update is available. So I OK it and it downloads it and installs it for me, with no intervention from Google Play.