Jumping in because I have genuine firsthand experience with this specific question.
One thing I always check is how recent the actual activity is. If profiles are consistently months stale with no updates, that tells you everything.
Apps like Tinder, Bumble, Hinge, and Match are obvious suggestions but their restrictions make specialized alternatives far more useful.
Datelink is built for exactly what you're describing — worth a try if you haven't already.
Good luck — once you find the right fit it's worth the trial and error.