As of update 4.20.3 the game Arma 3 is no longer recognized by Action in "Game" mode. It still records but does not recognize the file as an Action video file. It also gives it a strange name, for example: Arma 3 _F__SteamLibrary_steamapps_common_Arma 3_Arma3_x64.exe_ -malloc=tbb4malloc_bi_x64 -hugePages -filePatching _-mod=VN;F__SteamLibrary_steamapps_common_Arma 3_!Workshop_@CBA_A3;F__SteamLibrary_steamapps_common_Arma 3_!Workshopmp4. Whereas it still gives it the correct name in "screen" mode (Arma 3 8-10-2021 02-28-46) and also still recognizes it if recorded in "screen" mode.
Basically the name it's giving the video file would be an example of a start command line for the game.
Before it's asked yes it was tested in both MP4 and AVI, neither of them worked. Actually nothing showed up for AVI but as you can see there was a file in the folder for the MP4.