Bingo, eureka, you were right, the issue was with winfsp not being installed in the host.
For rclone to work in a Windows docker container, WinFsp must be installed in the host AND the container.
And the container run with the --isolation=process parameter.
As stated in black and white here WinFsp Container Support · WinFsp
The reason it worked on Windows 11 is I'd been playing with rclone before trying it in a Docker container.
Thank you for your help and pointing me in the right direction.