I see, sorry, this was my mistake.
I thought I could save a few mb filesize by not packaging in the extra prerequisites installer, assuming most people would already have those files insalled on their systems from playing other Unreal Engine games.
I have added them in the packaged zip file. Unreal Engine automatically bundled the installer in the folder:
ObservationDuty64\Engine\Extras\Redist\en-us\vc_redist.x64.exe
In case the launcher does not automatically run this.
Thank you very much for your message!