Recommending an alternative is not so easy, it really depends on how you've been using Strava.
Have you been running, cycling, triathloning...? Did you use it for route creation and discovery? For data analysis to support your training? Just for keeping track of your own activities? For segment leaderboards and KOMs?
If you're talking about cycling: I'd say MapMyRide or Komoot for routes; TrainerRoad or TrainingPeaks for analysis and training support; Garmin Connect for tracking rides, and I myself just decided to give Velo Hero a try (I find Connect to be very confusing). Segments and KOMs was Strava's only real USP because of the network effect and the wealth of data they had.
(Look, I'm already talking about them in past tense...)
This is all made a bit harder since Tapiriik, the file syncing tool, was disconnected from both Strava and Garmin Connect, for reasons I do not know.
At least Strava provides a way to export all your data in bulk (which now also includes power data for cycling).