I am using SPACEDESK https://www.spacedesk.net/ as an extra monitor for my Fire Tablet. It's free and it works seamlessly as it was an extra monitor. I have configured it as 3rd monitor, because I already had one. You can position it with Windows 10 "display settings" as any other monitor.
Once in a while it crashes, but not so often....
Priceless!
Once in a while it crashes, but not so often....
Priceless!