No one really cares about this "hidden rule" to be honest. People are extremely open about themselves on platforms like X and even Discord, primarily because they, like you said, have zero problem with showing their true selves, especially on social media platforms. And if you go on "those websites" like Rule34.xxx, people on there are VERY open about what they're into (iykyk). But yeah, there's absolutely no point in reminding anyone this as they likely won't care.

Instead, what you SHOULD hide when posting online is personal information that can easily be used to identify you (credit card information, email, phone number), that's why YouTube channels blur them out to keep those people's identities completely anonymous. If you accidentally leak your personal info, it might be too late as scammers might have already stolen your identity and done irreparable damage to your credibility. Moral of the story, while it's okay to show specific things on the internet, but not ALL things. Sorry for yapping, but I felt like I HAD to give my personal input.