Cannot delete columns


I run a Non Dynamic View sheet and have two checkbox columns that I cannot delete. Sheet states they are used in one or more format rules. Having checked all 14 formats they are not - nor are they part of any automation, form, cross sheet link, project setting or primary column.....

Here's the kick.

Cell history says those that were checked were done so by Form User. While they were part of a previous form that form was made inactive in May, most recent check box was Oct 13th. The new form does not reference these columns. copy/paste the old form link & as expected - Sheet is inactive, have since deleted.

I've deleted all checks and saved the sheet then renamed the columns & changed their function to Text/Number and saved again. 4 rows lit up with false? - there is no formula in the columns or cross sheet links and of these rows there was no commonality that would explain false.

I tried to delete the now renamed and blank columns and again sheet says Used in conditional formatting...

I'm at a complete loss - Yes I can hide the columns but in the past few days I have done this to 5 other columns not in use and they keep unhiding - and not by users (question for another time)

I'm at a complete loss on how to delete these two columns - Anyone else same issue or can throw me a bone?