There are VNC clients on iphone / ipad - but generally it's whole desktop.
RealVNC is the name brand but it's not exactly a good experience. "Screens 5" looks like a better alternative.
RealVNC did not work from iOS/iPadOS to macOS Golden Gate when I tried it relatively recently, although it may have been updated since. It's possible Apple changed something in their version of VNC's auth.
I used to recommend Screens (v4) when it was flat licensed, as it seemed to work well and was well designed in dealing with smaller screens and input differences. Now (v5) it's $5/month $30/year $200/lifetime, which I can't really justify for my casual use case.
At this point it almost feels intentional on Apple's part for not having a first party app, as if having one would be a tacit admission that iPads/iPhones are lesser than actual computers (although the logic does break down since they allow it on Macs).
IIRC they do support weird versions of screen sharing and remote control when on a Facetime call which is convoluted to say the least.