To go back to your OP.
If your lack of sharing does come up in a 1-2-1, I think you have a few options.
Firstly, you could go quite confrontational and get them to see that they're being U in asking you to share.
So say something like "What type of information don't I share enough?"
Then you say "So, you're reprimanding me because I don't tell my work colleagues all about my hobbies, family, whatever are you?"
Secondly, you're still a bit confrontational but you keep the focus on work and your ability to do your job. You something like "Me being a private person doesn't impact on my ability to carry out my assigned duties". You should be quite blase and make clear that you won't be changing this.
Thirdly, you tell them that you have very personal reasons for keeping yourself private. You can then either tell them the truth that you've been bullied in the past and won't risk putting yourself in that position again - the least people know the better. Or you just keep it vague - "I have very personal reasons for not sharing details of my private life". If they ask what, you can just say "I'd rather not say".
Fourthly, depending on whether your employer is a wanky, happy-clappy EDI one, you could say something about struggling with some significant identity issues at the moment and "feeling unsafe" in sharing them. Any mention of being "unsafe" sends employers into meltdown these days
I guess it depends how confrontational you are. The point is that sharing personal information isn't in your contract, not sharing doesn't stop you doing your job well and you should be under no compulsion to share anything non-work related about yourself. How you communicate that is down to you and how much of a mardy cow you are 😅