Sure, use your favourite app to track your workout and upload it to wanderer afterwards. It also supports auto uploads through a folder. So you can just place your workout file in the folder and wanderer does the rest.

Would this work like an open-source strava alternative?

It depends a bit on your use case. If you want track your progress on certain trails/tracks, then yes. Although, wanderer currently does not support metrics like heart rate or calories.

wanderer comes with a strava integration that helps you sync your data from strava to wanderer.