Customize the conditional formatting formula for the cross-sheet reference

I currently have a worksheet that compares three work columns with conditional formatting. The goal is to determine if the same string can be found in all three columns 1, 2, or 3 times. I have used the following conditional formatting formulas = countif (A: C, A1) = 1 and I have 2 more formulas with me = 2 and = 3 At the end. It works perfectly for my needs, unless I want to sort / filter each column separately, which seems like Google Sheets does not seem to work. So my idea was to separate each column into a separate sheet. The only problem is that I can not find the right way to format the conditional format in landscape format and still get the required results by distributing the same information 1-2-3 times on 3 sheets. I tried something like this = countif (Sheet1 !: A, A1) = 1 But it does not seem to be a valid formula, and I have to check all three leaves, not just one. Basically, I want to replace the A: C part of the original formula with Sheet1: Sheet3 but I'm not sure how or if that's possible. It may not even be an option, but I thought this would be the place to ask.