Hello
Thank you for your question and reaching out. I can understand you are having query\issues related to GPO settings in RDS or RDP.
If you set GPO for User level then it should be also applied to Published apps as Users will first login to RDS then Published app will be open , Hence GPO settings should be applied during that process.
For Printers Add a security group 'Deny Printing' to all printers with the setting Print -> Select Deny. Use GPO to 'Disable the addition of printers' for this group.
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