The message you are getting is because the user who is logged in already has an unattended license allocated to his/her user in Orchestrator.
You cannot use the same used to create a different robot in Moder Folders as the user is activated and linked to a given robot machine already.
Another reason why you are getting the error message is because UiPath wants to ensure that unattended robots are not disturbed by other licenses (floating licenses) say a studio pro. This message is just to deter users from allocating a machine as unattended but also trying to use the unattanded machine as another robot type.
So the solution here is:
If you want to allocate the robot, say studio pro to the same user you can deallocate the Unattended license to the user for a while until you finish using studio.
We do get this error in one of our environments in default folder. The license clearly says we can use it for troubleshooting and UiPath understands that we cannot purchase a dedicated studio license and have unattended license at the same time and when we have to hotfix bugs in production, we require studio access.
As you will notice, you do not need any license, your studio will open and you can edits workflows there. Just ensure you use it for troubleshooting and not developing workflows in the production environment.
If you are using default folders and have purchased studio / studio pro then you just do what is necessary. Do not worry about the license warning, there is no other alternative, which I / we known of.
Let the license be allocated as it was earlier. Do your required edits even if you get this warning. It is after all for troubleshooting purposes.