another non-notification thread (hear me out though)
I suffered from the non-notification issue that many KEYone owners have been complaining about. I've owned probably 50 Android phones since OS2.1 (rooted and unrooted) so I am no stranger to the OS and it's inner workings. After tooling around with my K1, I came across a part in the settings menu that I've never seen on any of the 50ish devices I've owned so I did a little playing around with it and it seems to have solved my non-notification issue, knock on wood. I probably had twenty or so apps that were suffering from this issue and since I played with this menu and its contents, every one of these apps has handled notifications correctly without keeping them open in the background.
The menu is as follows: settings-apps-gear icon in top right- special access (at bottom)-unrestricted data access
In this menu, I clicked all the applications on my phone that I have set to notify me in some way or another.
Like I said, everything on my device is working correctly, I can't promise that yours will but it's worth looking into if you haven't already.
Don't know if it makes any difference but in that same menu under background apps, I have the same apps clicked there as well. Doesn't affect my battery performance one bit. And of course, in the battery optimization menu, these apps are not optimized, as they shouldn't be.
I'm curious to see if this is working for others.