My Wii U started to not display 1080p or 1080i resolutions in the TV screen
I used my Wii U at its time ages ago but I didn't use it for basically 8 years. I started using it again since February, and some weeks after I started using it, the TV screen started to flicker. Flicker in the sense that it turned black or the TV acted like if the screen wasn't connected. Days kept passing to the point where the screen just didn't appear anymore.
I changed the resolution in the Wii U settings to 1080i which worked fine for a while, but then started to flicker/disconnect too. Then I changed it to 720p and it has worked perfectly so far from what I've noticed. I tested with different HDMI cables, in a different TV, and in either set up the problem keeps happening. The first TV where this happened reads a Switch perfectly, both with its and the Wii U's HDMI cables, and that was the same TV that displayed the Wii U perfectly ages ago and in early February anyways.
So I know it's not the HDMI cable nor the TVs. I know it's not the actual Wii U's HDMI port either, because if it was then it wouldn't display anything at all, but it does display 720p and 480p. Thus it should be something from inside of the Wii U.
I searched around about this problem. I saw some posts that were around 10 years ago saying that you should send the system to Nintendo (which is not only not possible anymore, but was never possible anyways where I live) and that it could be a fried CPU (which I doubt as the rest of the console is working perfectly and the 720p resolution displays without errors too). However newer posts about what appears to be the same problem say that it could be because of the system's HDMI chip, or the Panasonic IC or the coils around it.
My main questions here are: What is the exact reason that is causing the problem? Whatever is the reason, could I fix it, by say buying a new system component and changing the faulty one with the new one? And, is the system in danger of having its whole TV display damaged eventually? Because for instance 720p is working fine so far, but could it be damaged later too? Or 480p? In the worst case scenario I have an AV Wii cable that I could use, though not an AV to HDMI adapter, so I guess I could survive with AV 480p in case the problem is in the HDMI side only.