[...] EDIT: Figured out what is killing it off. Installing the Magisk module AppSystemizer seems to break the devbase completely. So now I just need a method to make an make a user app to a system app. If the YouTube app updates from the PlayStore it will break the app replacement and just load the new version. Uninstalling the update and rebooting seemed to fix that. Uninstalling Systemizer module did not seem to help and DevBase remains broken. So - I'm going to reinstall - and now I know what is causing it (hopefully) - I shall report back.
I tried Systemizer today and it didn't broke anything... it's really strange
[...] Now i just need to make Action Launcher a system app without breaking everything again lol. Do you have a recommended method for converting a user app to system?
Anyway - this entire situation inspired me somehow and I'm working on possibility to add new app (via /data/devbase/system/(priv-)app) - even if it does not exist physically in /system/(priv-)app. It will be a solution NOT dependent on Magisk. The method I'm thinking about will be suitable only for custom ROM like this DevBase, but it is enough, isn't?
In short - you will be able to add e.g. AppLock (with its original name) to /data/devbase/system/app, perform necessary changes in /data/devbase/system/csc/others.xml and AppLock will continue working even after install an updated DevBase
Please give me a link to exact version of Action Launcher you are trying to install "systemlessly". I will try to play with it tomorrow