Since you are still relatively early in the process of the development, you might be interested in some prompts.
There are about two ways you can frame the Exhibitionism genre: Do you want to stay hidden, or do you want to expose yourself?
The first kind of game is the most straightforward to develop for. It is all about navigational stealth challenges or puzzles. Try to reach one or several location nodes without being seen naked. This format benefits from small and tight levels with predictable NPC patterns; sometimes just getting from one side of the building to the other can be a sufficient scope. The main gameplay will be avoiding stationary or patrolling NPCs. You can spice it up with pickups or 'shields' that slow you down and raise suspicion but protects your 'confidence' enough to pass areas without cover.
One example that comes to mind for that is that Nagisa Kusanagi game.
The second kind of game is basically a Social Stealth Sandbox, and it is actually a bit hard to come up with a gameplay loop that actually requires a wide open level. The best I can come up with is designing the challenges around getting into position, doing a stunt (or several), then escaping. Try to de-emphasize instant failure conditions; if you are not physically getting caught, you should be able to continue. Objectives should depend on the nature of the map; for example, if the map is sparsely populated, a goal could be to seek out a number of guys, give them a good scare, then shaking them off, and how hard you have to shake one off depends on whether they prefer to pretend minding their own business, whether they chase and search you, or call other people.
If that sounds like a lot of work for little gain, you'd be right. A lot of solo dev projects die on Open World design, since it is hard to not only come up with a fun game, but it is also hard to implement technically. Even Seleka/Manaka, for how polished they are (relatively), are bundled with a few questionable mechanics that are probably very poor fit for the genre. The health pool is too small to allow you to meaningfully engage with the social/crowd aspect, and the stamina serves more to prolong the traveling time rather than providing meaningful gameplay, since you 'die' too fast for it to ever matter. For how many locations there are, the objectives are at large just copy-pasted from one to the other. The games actually came out at all, which is neat, but it feels more like a game of the first genre with a lot of useless fluff attached that get in the way.
If you are still interested, then the first challenge to clear is probably to produce a robust NPC scheduling and reaction system. Make a test room for different kinds of reactions before throwing them into a proper map.