I have also accidentally closed the App in the middle of a workout. Usually if you reopen the app and click on the partially completed workouts it will give you the option to resume.
Yes, there is an option to resume an incomplete workout on all apps AFAIK. I searched, but can’t find an official support article. Maybe @IvyAudrain can check to see if I just missed it, or if this is an opportunity for TR to document the feature.
From memory, you open the incomplete workout, and may need to hit the ellipsis […] icon to find a “Resume Workout” or something like that option. I have done it on Win for sure, and I think I tested on Android mobile a while ago with success too.