I've seen a lot of very fit cis-women. I think if you choose to concentration your workouts on the muscles you want to keep the same or similar, then I do not think there will be a large loss. I'm speaking from personal experience when I say I kept the muscles I wanted... but this was for the abdomen, legs, and butt, which are muscles I do think most other girls prefer too.
If you have muscles, but you aren't doing anything about them or you are not working out, then I think they will start to decrease even if you are not on HRT. The decrease would probably be more rapid or noticeable with HRT.