@david I have the same problem for some other sports where Indoor FTP is not shown when creating the workout. I think this is a general issue, but here is my case.
I do cross country skiing (Nordic skiing) and with Garmin you now get skiing power similar to running power.
I also do indoor ski training on a machine with a power meter (SkiErg) and this will automatically be uploaded as Nordic Skiing. The powers for skiing outside and inside cannot really be compared as skiing engages your full body (even more than running) does that to a lesser extent. I therefore requested a separate activity for that:
Would it be possible to:
a) create a skierg activity,
b) add support for user/custom activities, or
c) add support for selecting indoor for all activities (or at least if both an indoor and outdoor FTP is defined).
Maybe b) could be a good option as the list of sports are potentially endless. Even for Nordic skiing you would normally differentiate between classic and skate as these will have a 10 % difference in speed, use different equipment, and very different in technique.