Yrp! Same for me. It happens very often since 1.80 Vanilla. My left Alt key toggle also very often in altitude mode in 3den editor (I just have to strike ALT one more time to toggle in normal ALT behavior. Arma is the only one software to do this weird thing.
I also experience some heavier freeze with no possibility to ALT tab and work on task manager as in video. I can just shut down the PC and restart it!
Is it linked to French keyboard? I guess not. To video card? I'll see that with further NVIDIA drivers, but I guess not. So, What BI/Steam did with the keyboard interaction??? Why does these problems happen on Arma only?

Defragmenting game files after large updates and user files, even for SSD, speeds up the game loading a little, but this also does not exclude the possibility of sometimes freezing games for me. Try to optimize the disks with the program Disk Defrag Pro, the program has the ability to optimize only files that have defragmentation. The windows disk optimizer for this task will not work.

@Lex So, it's not a solution and not related to 0% CPU usage and/or GPU freeze + ALT key malfunction in Arma only.

Seems Microsoft has put some weird stuff in the Fall Creators Update, I've been having different issues with other apps, i.e. https://gitlab.com/tortoisegit/tortoisegit/issues/3087

This issue can still be reproduced in the RC of 1.82. It is even enough to simply Turn Around, then immediately ALT-TAB to freeze Arma 3.

Still happening in 1.84