EDIT:
I appear to have resolved the issue by uninstalling some Dell software that was pre-installed on my workstation. Why or how that would interfere with InDesign I have no idea but colour this resolved.

original post

I'm having an issue with the Separations Preview panel not showing any percentage values, it's just blank. I think it started after updating from 20.3 to 20.3.1; but I installed versions back to 19.0 to test and it strangely seems to be effecting those versions too.

Widows 11, all updates current.

A web search showed this issue has popped up in that past and I follow the advice given (deleting caches fixed it for one).
I've deleted caches
Reset preferences
Uninstalled/reinstalled
etc.

Nothing so far has fixed the issue.