Plex player on Windows 11 shows black screen unless there is another window visible

Plex Players
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1

Server Version#:1.42.1.10060
Player Version#:1.110.0.351-4e48eb83

When playing any video on this setup onto my LG TV, the video starts and almost immediately displays a black screen. After a while it may move on a few seconds but will then show the black screen again.

The same content plays well in the browser version.

Video drivers are all up to date.

Any help greatly appreciated.