Hello @LangeMuller ,
Thank you for reaching out to Microsoft Q&A platform. Happy to answer your question. Please follow below instructions to disable multiple RDP sessions on windows.
Disable Multiple RDP Sessions :
- Log into the server using Remote Desktop.
- Open the start menu and type 'gpedit.msc' and open it
- Go to Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > Connections.
- Set Restrict Remote Desktop Services user to a single Remote Desktop Services session to Enabled.
(If the response was helpful please don't forget to upvote and/or accept as answer, thank you)