If you go above 4k you will start to hit a limit of most (older) hardware. To go above 4k you will have to start thinking about specialized solutions like oculus did with their 5k Henry video (https://developer.oculus.com/blog/behind-the-tech-with-john-carmack-5k-immersive-video/)
Btw if the scene in your video is mostly static you can also replace that with an high-res image and use small video’s for the moving parts.