Good privacy friendly fitness app?

gadgetbridge is the only one I know of.

It really depends on what you need. I use GymRoutine because I can track my training and that's all I need for that

i use paseo for counting my steps

Depends on what kind of app of course, but I've seen Progression (Android) recommended a lot around weight lifting online communities.

I've had good luck with FitoTrack in F-droid. I was looking for a drop in replacement for the workout app on Apple Watch, and that seems to do well.

I use Hardy to track my lifts

If you have iPhone, the fitness app on there is actually really good