How do I count the number of TEXTJOIN functions in a spreadsheet?

The result of TEXTJOIN is a null string "" if there is nothing to join. COUNTA is including the null strings, which is why it is counting what look like blank rows. Try COUNTIF(I,"<>") . This will count rows that are not null strings (or blank).

Replace COUNT with COUNTA and it returns how many values you have in column I

I replicated your scheme and it works for me it gives me back 5

Obviously COUNT.VALUES is in Italian, but it corresponds to COUNTA