@hammerhai I have this version check functionality in one of my apps, without firebase, and the app is also free of any extensions.
The way it works, is that there’s a variable LocalVersion that I manually set to the version code in every release (I forgot to do it in 1.1.1 and rushed out 1.1.2 to fix that 
) On Screen1 initializing, I fetch the latest version from TinyWebDB (also manually saved by me). If LatestVersion > LocalVersion, show uncancelable message alert with one button only.
Title: Update Available
Message: A newer version is here, kindly update.
Button: Update
When Update is clicked, open Play Store page of the app with an activity starter. Simple.
To force update: When other screens initialize, check version using the above given technique, and just close Screen instead of showing alert. (you can close Screen with end value, so that Screen1 clarifies why it closed, using another message alert.)
Hope it helps… Just one of many useful tricks in my app 