Existing feature request 4603 is something you'll want to have your SE add a vote to so that PAN knows you want this feature built into the firewall. At the moment this isn't something native to the platform and the best way to accomplish this is though a script that interacts with the API to ensure that the user only has the number of active sessions open that you feel comfortable with. This is a relatively easy script to make as long as you are comfortable with scripting and using the API in something like PowerShell or Python.
@pratChamp an example of a powershell scrpit that does this job I posted here: https://live.paloaltonetworks.com/t5/General-Topics/How-to-limit-concurrent-GlobalProtect-connection...
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