National keyboard reseted

I'm using Polish programmer's keyboard and this is the only keyboard installed in my OS.

Since a couple of days I have some problems - the ability to type national chars (left alt + letter) suddenly disappears. The only way to deal with it is to restart the computer.

I cannot associate any action with the moment this happens, like running a program, pressing any keys combination etc. I guess this started happening after installing Augusts security updates.

Can someone suggest where to look for the problem source?

Have you checked to see if there is an updated driver for the keyboard on the manufacture's web site ?

All drivers are up-to-date, I'm checking them weekly, both via Windows Update and Dell Update (both laptop and external keyobard are Dell's).

OK, I've got a clue what's going on, but cannot figure out how to resolve it.

Even though Settings tell me I have only Polish programmer's keyboard installed, when clicking Win+space I'm getting the language bar showing me also default US keyboard. I suppose that's what made me change the keyboard to the US one without national chars.

How can I get rid off this US keyboard if it's not available under Time & Language settings?

I also disabled all shortcuts to swap the keyboard, but the one Win+Space still works. I've temporarily disabled it with PowerToys, but I'd like to get rid of it permanently.