A workbook that has been running happily for 10+ years suddenly stopped honoring Conditional Formatting. When I say "suddenly", it was NOT with my advent in Win11 (6 weeks ago), but less than two weeks ago.
I checked the settings and yes, everything was in place.
Then yesterday an online bank web page stopped working.
I traced it down to a Win11 Themes setting - contrast, text colour, background colour, that sort of thing.
Changed the theme (or reset default) and Bingo! Online banking works AND values over a threshold are now highlighted.
In my opinion, another case of Windows either getting too smart for itself, or else Larger Tail Fins.
Cheers, Chris