Conditional formatting based on another sheet in Google sheets

Question

I googled for it and looked into many answers here, but it seems still not working for me.

I try to use this conditional formatting:

EXACT(A3,(INDIRECT("U_automatikus!A1:A")))

Here are the screenshots of my sheets.

Why it isn't doing anything?

My aim is to mark those in the first sheet which are present in the second too.

Answer 1

=FILTER(A1; COUNTIF(INDIRECT("U_automatikus!A$1:A"); A1))

demo spreadsheet