I have an app created for internal use. I have not published it on the play store, but I have to update it regularly.
Can anyone help...with which library should I use for implementing a self-upgrade system to my app. Any answer would be appreciated.
The answer is - yes, You can upload your app to the Apple Store and Google Play but Not publish it to the public, instead, you can use internal testing So only users that you define will be able to see or download your app in the Google Play and Apple Store
Google Play internal test https://support.google.com/googleplay/android-developer/answer/9303479?hl=en
Apple test flight https://developer.apple.com/testflight/
Yep it has some limitations, for example, Apple allows up to 10000 testers but I hope it's ok for your company, but its only way to share app internally without any issues on iOS (android allow you to download apps from anywhere, iOS don't)