I performed a repair installation of windows 10. Afterwards, I was able to start the Arma3 Launcher. It seems sfc /scannow and DISM did not repair everything.

Thanks for your help! My issue is resolved.

I ran the system file checker: sfc /scannow and when that failed to fix any files, I ran the DISM command to a locally mounted system iso image. It finished successfully, then I was able to run the sfc /scannow and it said it repaired a file. I ran it a second time and it said there were no integrity violations.

Lastly, In steam I did a "verify integrity of game cache..." and it found 1 file which it reacquired.

Still the launcher crashes, see the uploaded 'Round 2.zip'.