I just do not think she would mention it if it was a uniform thing done for everyone
I can think of two potential reasons. One, she didn’t know it was done for everyone, and two, she did but left that detail out on purpose.
I can’t think of a reason why palace officials would, if they didn’t do it for anyone else, decide that Meghan must be kept prisoner. What motive is there for this? And if this was the case surely it could be fairly quickly resolved. She mentions to Harry “I was surprised they took my passport, why did they do that”. He says “what?? They took your passport?? That’s not normal”, and then he goes and tells his staff to give it back. I’m assuming it wasn’t the case that this happened and he was refused, because I’m sure she’d have mentioned that. “They took my passport and even when Harry tried to get it back, he couldn’t, that’s how controlled I was.”
As I said, I can totally understand why she wouldn’t want to give them her passport. If I was in that situation I’d have balked at it. I think it’s a reasonable example to bring up to illustrate the sort of life they were living, and how different it is to “normal”. I just don’t think it’s reasonable to assume she was unique in this, and that everyone else had their passport in a drawer somewhere in a palace.