Count the number of unique numbers/strings in a column, but limit the set to the rows that satisfy a certain condition in another column

Question

This: "'=COUNTA(UNIQUE(D2:D724))"' works, but now I want to limit the input to this formula as follows:

only for the rows for which in another column a logical condition is satisfied, count the number of unique numbers/strings in column D for this limited set

So I want to limit the set D2:D724 in =COUNTA(UNIQUE(D2:D724))

I don't want to use filters for this, I want to do this with formulas.