You can stream 4k content on your tv but your tv will play it in 1080p. Your tv doesn't have enough pixels to display 4k. It will automatically play in the tv's max resolution.

Iinm, only possible for YouTube. Netflix will stream based on display output detected by the device(Realme 4K Stick).
You probably need 4K to 1080p downscaler.

The "wm size" ADB trick (a command tool for developers) to set a higher virtual resolution works for some apps like native games. The increased sharpness in the same 1080p display is noticeable.

Haven't had much luck with video streaming apps or Stadia, it would be better to use a hardware downscaler so you enjoy the higher picture quality of the 4K streams.

Did you find any reliable one? There are more models now but comments in stores usually point out there's lag or frequent black screens.

I used to do this with my computer, if I wanted the highest picture quality I would set YouTube for example on 4K and run it on my 1080p display.

You can do this and AndroidTV too. Click the triple vertical dots and select the stream quality you want.

Also there might be an advantage to run it through a HDMI splitter that will take a 4K signal and downscale to 1080p, but perhaps a random HDMI splitter doesn't have the algorithm to downscale with good quality.

Now you're confusing display resolution with video stream resolution. There's no need to do this.

The Realme 4K will automatically downscale the video to 1080p if the TV is only 1080p.