Filter inside Countif?

Hello!

I have a spreadsheet with a GANTT-look-a-like sheet. (mock-version attached).

I can use COUNTIF and get all non-empty cells or cells that contains something. BUT that isn't dynamic, FILTER can do the dynamic part. Like specific dates.
But I can't use COUNTIF(FILTER)? And get the amount of results?

I found something about sumproducts but cant get that to work. Any help?

(The yellow part is where I need help, can probably do the rest if I get that part right)