I have the same issue.
Group contains such field: securityEnabled.
securityEnabled
So if securityEnabled=true - requests with allowExternalSenders,autoSubscribeNewMembers,hideFromAddressLists,hideFromOutlookClients will fail with 401.
allowExternalSenders,autoSubscribeNewMembers,hideFromAddressLists,hideFromOutlookClients
https://stackoverflow.com/a/63529694/11231972