The current indoor running app is mainly for treadmill.
What about indoor track runnning where GPS is of no use (though i think the app could benefit in outdoor running as well)
I base my ideas upon the clever Race Screen https://apps.garmin.com/en-US/apps/6a30651b-ca67-41a5-96dc-60634983fc93
I imagine you could set on before hand how long a lap will be, 180, 200 or 400m. Some indoor arenas vary in length.
Then if you run an intervall workout or threshold workout you could calibrate on the run with the lap button. Imagine the watch meassuring 190 out of a 200m lap, you press the lap button and it corrects to 200 and adjust lap pace. or if it measures 210m it corrects downward to 200m. Its useful because on threshold runs on indoor tracks during winter I often measure effort by lap time ie 48s/lap for a 5k/25 lap event on a 200m track.
Ultimately i think this feature should be built into the garmin but if anyone is up for grabbing the idea then please :)