Hi Marko,
Thank you for posting your query. According to your description, you have tried editing the group policy. To achieve your goal, you have missed some details. Here are some suggestions.
To set the group policy correctly, you can refer to this official document.
Configure Timeout and Reconnection Settings for Remote Desktop Services Sessions
https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/cc754272(v=ws.11)?redirectedfrom=MSDN
To know information about sessions on a Remote Desktop Session Host (RD Session Host) server, you can refer to this link.
https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/cc731503(v=ws.11)?redirectedfrom=MSDN
The key point to solve your problem is setting a new GPO. For you want some particular users not to be teminated, setting GPO and then apply the group policy to this GPO is of great importance.
To set up a new GPO, you can refer to this link.
https://learn.microsoft.com/en-us/windows/security/threat-protection/windows-firewall/create-a-group-policy-object
---If the suggestions above are helpful, please ACCEPT ANSWER. Really appreciate. This will also help others with similar issue to find this post quickly. ---
Best Regards,
Grace