Simple command:
Set-DistributionGroup mitarbeiter-xx -BypassModerationFromSendersOrMembers @{add="mitarbeiter-xx"}
With this command the members of the distribution group are added to the bypass of the moderation of this group. This command delivers no error message BUT it simply deletes every existing bypass entry AND doesn't add itself. If the command is used normally without @{add= then the command works but it replaces instead of adding so it isn't useful for my purpose because I need to add members via batch to several groups.
Via ECP I can do this without any harm.
Same syntax with -moderatedby is also working like expected so I don't seem to have an error in my command.
This should both work like described here: https://docs.microsoft.com/de-de/exchange/recipients-in-exchange-online/moderated-recipients-exo/configure-moderated-recipients-exo
Maybe someone could test it on his side if the same thing happens. We are using Exchange 2016 on premise.