Relive actually does support GPX upload and touts it as a way to still integrate with Strava, albeit by manually downloading the gpx from strava and uploading to relive:
https://support.relive.cc/article/18-import-old-activity
Good to know because I don't want to have an account on Strava or similar services. I didn't notice that import functionality when I created my account, only the prompts to connect to third-party services. I'll create a new account and check it out.