I'm pretty sure. The reason being is that there is currently no google device running Android that supports external 4k output (Chromecast ultra isn't Android). Every device that does support 4k output through HDMI has had to shoehorn it in with their own drivers and kernel work. Now imagine the Chinese company making these Android boxes dealing with this issue but with SOC's that are not open sourced or have very little support from the developer. It's impossible to get done. I looked up a couple boxes running those chipsets you mentioned and they strictly state they support 4k decoding. Nothing about output.

Edit: it looks like some boxes with the s912 has 4k 60hz output. But at the price your better off getting the mi. https://www.amazon.com/Beelink-GT1-Cortex-A53-Mali-T820MP3-Streaming/dp/B01KFMLCX6