I "upgraded" to Windows 11 and discovered that Microsoft are using Windows 11 to kill off Internet Explorer. You can sort-of run IE inside Edge but functionality seems limited and it is only for 30 days (not sure what happens at the end of that 30 days).
Luckily rolling back to Windows 10 is easy enough.
So if you want to keep using this game don't upgrade to Windows 11.
Unless of course I missed something! Suggestions from clever people welcome....

You can use the app, without going through a browser. Works perfectly.

https://www.funkysnooker.com/build18107/application/funkysnooker-18107.exe