Main screen isn't working

Ik this is a very very response late but the exact same issue happened to a secondhand Zflip5 I bought, and since this could be a very common issue it might help others in the future as well.
So basically if there's damage on the hinge, the flex cable connecting the two sides could be broken causing parts of the screen to malfunction or not work at all. Samsung put the screen connecter on the lower half and decided to connect it to the motherboard through a very fragile flex cable running through the hinge for some weird reasons, so any damage on the hinge or even just too many folds can cause this cable to get worn down, torn and cause things to malfunction. For me it was the phone shutting down completely when I fold it because the cable has fractured, but the same cable could be causing the screen to malfunction for you.

to test whether the cable is broken you can just purchase another cable and attach it directly outside the hinge (as replacing it would require screen removal and is messy in general) to see whether the issues disappeared. If not then the screen is damaged (it is very fragile after all) but if the cable fixed it you can then proceed to replace it and restore its functions.