Keyboard doesn't work - weird window pops up in the middle of my typing
 

This is what pops up:

https://ibb.co/2sn6BBr

https://ibb.co/2sn6BBr

<a href="https://ibb.co/2sn6BBr"><img src="https://i.ibb.co/CM1tFFy/Screenshot-20220624070512.png" alt="Screenshot-20220624070512" border="0"></a>

How do I get rid of it?

how often happened it? did you try to close that window (ESC)?

You accidentally activated a key combo that pops up some sort of app launcher.
Please check your desktop environment's settings for where hotkeys/keyboard shortcuts are configured.
OTOH, It's also possible that this app binds its own key combo.

If you have further questions, more info about your setup is required, esp. the desktop environment.

It happens very often, two or three times during my lessons.
And also, after it pops-up, the keyboard changes back to English (although I changed it to Serbian, or German)

And yes, I did close that window, but then, I dont get the recovered document.

Know that. Don't know which kind of combo that is, since I type very fast.

How do I do that?

I don't know what OTOH means
How do I get that info?

I gather from the screenshot that you were typing in Firefox when this happened.

You might try starting Firefox from the command line. Then whenever you get this popup, you might get some output to the terminal which will give you hints as to exactly what this popup is.

No, I don't use Firefox, I have to use Google Chrome because of my work (the platform I work on has issues if I don't use Chrome). It also happens when I use LibreOffice, and also when I write messages in Zoom.

I guess you need to find out which key will bring up that dialog first.