Me too my sim is wearing his robo-arm, a white t-shirt, the black standard underpants and the trademark university black and red boots. I tried to plan his outfit to add some Jeans, but the robo-arm vanishes in CAS.
So I've tried changing to nude, then go back into change outfit again and it gives me an option wearing the black jeans He was wearing before. Hope this helps a little as I still don't know how to remove the robo-arm yet.
I'm also having this problem. Curiously, if I have a second robo-arm in my sim's inventory, I get the "Place in World" interaction when I click on the sim (this doesn't remove the robo-arm though, it only places the additional robo-arm from the inventory). I have mods installed, but I have tested it with all mods disabled and the issue remains.
