Cosplay is one example. There’s a handful of NSFW ‘cosplay’ communities, one not-very-active one on blahaj, and one squatted on .world by a user who is also squatting a whole bunch of clearly NSFW communities and has never posted or commented anything anywhere, and named themselves “@Moderator.” Laser cutting, Inkscape, some book fandoms are examples I was (and to some extent am) actively engaged with on Reddit where communities exist, but are far from a critical mass.
Data privacy isn’t to protect you from getting caught doing wrong things, it’s to prevent malicious actors from having the information to manipulate you. You don’t want phishers to have access to your life details that security questions ask about, even if each one is nothing to hide. You don’t want scammers to know where you went to school, who your teachers were, and what clubs you were in to build up a convincing backstory for their facade. You don’t want someone who wants to get something out of you to know who is important to you and threaten or impersonate them. It’s not about having something to hide, it’s about hiding personal details from those with malicious intent