There are a very minor amount of open source services that you can run yourself on a server in your basement. I'm sure they do nothing like Apple will do for you with fancy dashboards and stats but they can collect the data you create.
Here' a bunch of them (pardon the reddit link): https://old.reddit.com/r/selfhosted/comments/14wxful/open_source_fitness_tracker_w_self_hosted_fitness/juswr05/