@blackxpade, attach files by dragging and dropping them rather than pasting a wall of text.

Try restarting your computer and then verifying the integrity of the game cache for Arma 3.

Hello blackxpade,
the logs says that Launcher can't start because it can't load the file D:\Steam\steamapps\common\Arma 3\Launcher\log4net.dll.
Did you tried to verify the integrity of the game cache as Jawsh suggested? It should force Steam to re-download any corrupted or missing file. If the issue will persist after that and the file exists in the directory (as written above), please try to delete the file and verify the game cache again to force the re-download.