Hello G Musgrave,
Welcome to Microsoft Community and we regret the inconvenience caused to you.As you mentioned it all happens randomly because sometimes it works fine and sometimes it doesn't... When you go full screen and it goes black I think you can bring up the Task Manager via Ctrl+Alt+Delete and find the running game and select End Task. It won't solve the problem but it can save you from having to restart PC every time. According to your description you have also tried many troubleshooting steps. I don't know how long this problem has been occurring, was everything fine before? Assuming everything was OK before then please uninstall Windows updates to try again. Use the following steps:open SettingsUpdate and security >Windows updatesClick Advanced optionsClick View your updates History If you want to Uninstall updates, click uninstall updates on the top, the page installed updates would open and you can uninstall updates easily by right clicking the specific update.
OR
Just type in Installed updates in the search bar on the taskbar and Install updates would be shown, which can also be used to uninstall updates. Likewise, please check the version of your graphics card driver. If there has been an update recently, please roll back to the old driver version. If there is no update please keep it up to date.Another possibility is if there is a malfunction with your graphics card and motherboard, such as cooling issues or hardware failure. It will also happened.This is advice based on my experience and I hope it gives you a direction.Wish a good day!
Best Regards,
Lenka-MSFT| Microsoft Community Support Specialist