How do you delete VR apps in the Unknown Sources library tab?

I was wondering the same and so far the only way to do it I've found is via adb with the device connected to your development computer. You can just do this (change com.example.app to the identifier of your app):

adb uninstall com.example.app

Good job！

You could also consider to install a file manager that comes with an app manager. Is useful for more than that during development.

I ended up getting this app:  https://headjack.io/tutorial/sideload-install-app-apk-oculus-go-quest/
It's worked great.  Some apps I've made have crashed badly and won't even show up in Unknown Sources.  This app still finds the bad apk and allows me to remove it from my Quest -- something SideQuest failed to do.

Under settings and storage (in german "Speicher") you can find all installed apps, also the ones from unknown sources. There you can delete them, too.

If you're in the Quest Link menu (in headset): The same way you uninstall all apps, pointer over it, select the three dots "..." and then select "Remove from Library". If you don't see the app listed in the Quest Link library, disable it and do the following:

From the standard Quest Home (in headset), select your Library (9 squares icon on the toolbar) then select Unknown Sources on the top-right dropdown menu (last on the list), and then select the three vertical dots (... but up/down) and select uninstall.