Try guiscrpcy. https://github.com/srevinsaju/guiscrcpy

my apps are set to unrestricted.

This is the strange part.

But well, if you've done everything suggested here and it still doesn't work, you have no choice but to live with it.

Oh, that's for sure the system. But nothing too crazy if their background process are not set to unrestricted.

You may want to check Playservices as well, especially the main activity.

If It gets killed often and not getting restarted, it could be a problem since they are pretty much responsible for handling cloud messaging.

My bad, I didn't mention it yet, What I meant by constant values ar the number after subreason= or reason= lines.

Do you see them? What are they mostly?

Find what actually kills your app by running the following line via ADB terminal.

adb dumpsys activity exit-info *app package*

That gave you a list of the "killers" of your apps. The reason or subreason constant value can be checked here.

You haven't mentioned this in OP yet, try to lock your apps from recents and enable autostart for them.

It suprises me that the guide for Samsung at dontkillmyapps is so long lmao.

There are two options that makes me a bit confused.

Auto update apps. Try to install updates automatically

Notify about new versions of applications. Show a notification when new versions are available

Do I have to turn off the later to let the auto-update runs fully in background or It's fine to keep both enabled?

On the first run, I think I had both enabled and I still tapped multiple times. Shizuku installer worked great though.

They don't seem like they have background installation mechanism right?

I went all of the troubles creating an automation with Tasker because I haven't found one that worked like Google PlayStore's auto-update back then.

I wonder if there is a couple of them out there that already has those? Maybe like with shizuku, ADBwidi, or root access?

Edit: typo