Disabling each and every "picture improvement" setting (including HDR both on the TV and the input devices) to get the most neutral picture possible would be my priority. Dizziness while gaming could depend on the game. Some games are not playable for me even on otherwise known-good hardware. Motion sickness can cause dizziness, but perhaps you can rule that out. The Fauser LiFli flicker detection device due to its acoustic feedback helped me to identify flicker that I would otherwise not have spotted on my backlit TV: flicker during black screen content, that happens during ads, when switching inputs, in between input resolution changes or short breaks in movies or black loading screens in games. I doubt this specific issue would happen on an OLED screen, but who knows. Those bursts of flicker are short, but if you know when to look, it should be recordable with cheaper oscilloscope setups, too. Contrast enhancing features can cause dynamic flicker during certain scene content. Any "automatic" contrast or brightness setting is prone to using flicker. Some form of flicker detection equipment always comes in handy. In particular for finding the exact brightness value that causes PWM to kick in. Try to avoid that by not setting the brightness too low.
Another thing is disabling the TV's status LED and other connected devices' LEDs if possible. They can flicker, too. Or gamepads that have built-in LEDs. The PS4 gamepads definitely flicker. Probably same with PS5 and maybe other gaming hardware. It helps if you know the devices you use to play games and watch movies are not the cause for the dizziness - e.g. by using them on a known-good TV or monitor.