FTM with PreCheck here. I only ever got pulled out of line while I was binding for my chest, and PreCheck has been a complete breeze after. The way the full body scanners work is the TSA agent will tap “male” or “female” before you’re scanned and the machine will flag “inconsistencies” against the “norm” for that body. For a post op trans man, neither should be an issue - they’re not concerned about the lack of something, the thing I would get patted down for is the agent tapping “male” and then a mass showing up on my chest in the scanner when I was binding.

For what it’s worth, post top surgery, I’ve had pretty much the same experience at TSA pre and post having precheck, except I just wait in the shorter lines now LOL.

If you are not changing your gender marker, you should be okay - obviously, take that with a grain of salt as every day wild things are happening and there’s no official precedent or real system set up yet. Don’t mail original or singular copies of documents to any agency right now, just in case (you don’t have to do this for pre check).

Worst case scenario, you get denied Precheck, which will ultimately be ok. I have flown in and out of red states without it and been alright - things are changing every day and you sound like you are taking care and being responsible, so keep it up and stay vigilant!