Hey there @basti_quader,
This issue has been fixed in Rhino 8.25 which is available as a service release candidate, or there are workarounds listed here → Error Installing at Paketmanager - #2 by CallumSykes
Ticket is here → https://mcneel.myjetbrains.com/youtrack/issue/RH-89655/PackageManager-install-dialog-not-showing-buttons-on-Mac