@MCA_der_Negus I'm so glad to hear that getting rid of all those service sims helped. 78 is a much more reasonable number, and unlikely to affect how your game runs, although it still seems a bit higher than normal. Some of them will of course be the usual service sims that need to show up when called, either by you or the game, e.g. maids, firefighters, babysitters, newspaper and pizza deliverers. But it's entirely possible your save is still generating too many of them to fulfill some other function, and that without intervention, you'll wind up in the same place you started.
If you want to find out where they're coming from, you can get info on any particular sim via MC. There are probably several paths to do this, but one is (City Hall) NRaas > MC > Sim > Status > Career > Town Family > Service. Once you select a sim or sims, you'll get a report on each one listing their assignment type. If you see that one type has too many sims, or that a bunch of sims don't have any type listed, you'll know they're the problem. (A couple of sims without an assignment is probably fine; a new game I just started had two. They're probably just waiting to be assigned as coworkers or drive carpools or something.)
One potential source of service sims that I didn't mention before is the set of homeless street performers (acrobat, magician, singer) spawned when Showtime is in play. The issue is not that the performers exist, but that the game keeps assigning new ones, and possibly bumping the old ones out of their assignments, meaning they wouldn't be listed when you searched using MC > Demographics > Type of Service. There's no real way to stop this the game from generating these sims; even mods can't shut it down entirely. So the only useful approach is keeping an eye on the numbers and getting rid of the extra sims when necessary.
On that note, NRaas Overwatch has a setting to remove homeless sims that aren't currently assigned to a particular role. Sometimes it's a bit too invasive, as in, it might remove sims who exist for a reason that OW can't currently find (for example, the workers staffing the seasonal festival booths don't have anything to do the rest of the year). But it's an easy setting to test, and it wouldn't require you to manually sort or delete any sims. The path is (City Hall) NRaas > Overwatch > Settings > Clean up all Homeless > True.
@puzzlezaddict I cleaned up the homeless and it seems that it doesn't grow anymore. Thank you again for your huge help. I never thought the game could be fixed without a complete reinstallment.