I originally thought the issue might be a question mark was in the activity’s title, so I removed it. Sync still isn’t happening. I also don’t see a way to upload a GPX or FIT. Thanks.
I did the “Sync Single Strava Activity” before and after removing the question mark, but it appears to have failed both times.
so I just figured out a workaround. it’s hacky as hell but it worked.
I uploaded the workout FIT file to runkeeper, which I haven’t used in ten years, and synced from there. Worked like a charm.