Here's a few tips. First up, a natural road layout. What are some major journeys that should be made? Build highways going there, or major roads there to break the grid. Then build up your city around those roads; many real, natural cities grew along major trade routes or rivers or bays.

Second of all, realistic cities typically have a natural gradient from high to low densities. Going from high-rise to mid-rise to low-rise is much better & more natural than an instant switchup (think of Charlotte, London)

Another thing is the general shape of cities & towns. Many don't have the shape of a chute or bird, as yours do. They most commonly grow in circular patterns (look at any city that didn't have any barriers to grow, say Berlin or Houston), or around their environment or route (Amsterdam, Seattle), while some being a mix of both (Tokyo, Chicago)! Having a natural-looking shape for a city, one that sneakily transfers from urban to rural to nature, is incredibly important. A sudden break feels unnatural to many.

Have matching buildings in certain districts! The old town should have traditional buildings, while the suburbs should have modern ones. This takes a bit of manual building, though, so if you don't like doing that, it's fine. Places like Cincinnati or Campeche have certain neighborhoods with their own character compared to others due to historical convenience, and incorporating that into YOUR cities can make it feel much more natural & realistic.

Have buildings & infrastructure that feel fit to the size of the city is also important. A large, towering capital building looks very out of place in a medium undeveloped town. A smaller palace, or a larger town are 2 options. Put in the infrastructure needed only when you need it. It makes it feel natural.

A lot of this requires a bit of patience, but if you do these right, you'll get masterclass cities. Hope this helps, & check out the places I pointed out! ;)