When I make a remote desktop connection to another Windows 10 PC, it puts coloured boxes on the background of any programmes, including Windows settings.

This is an issue with the client PC in that it shows on multiple remote PCs through the same client and does not appear if I connect to the same remote PCs from a different client.
I updated Windows 10 today before this started happening.
There have been no other changes since this was working properly.
I only see KB5000842 on the list of updates, but it won't uninstall.
When I tried to rollback the quality and feature updates using Recovery > Advanced start-up, it said that neither could be uninstalled.
sfc /scannow found no problems.
Any ideas what can cause this?