Filtering apps by license is a great filter for intent. There are many reasons people write FLOSS licensed software for, but the fewest include wanting to get your data. For economically thinking professional data collectors who e.g. put some dancing pigs game out to get your contact data, the gaining access to a small population aren't worth the effort of open sourcing. F-Droid also has the concept of antifeatures, which upfront informs users about potentially unwanted behaviour like tracking.