In theory, you need a scaler.
The mClassic is the option I went with (and that I see most often recommended):
https://smile.amazon.com/Marseille-mClassic-Plug-Console-Upscaler/dp/B07X6KDQ98
Really great detailed review and FAQ to bring all users up to speed. One thing I would like to add is if somebody finds a device that doesn't work with the Rokid Max (Nintendo Wii U, PS3 game outputting 720p, xbox360 game outputting 720p, 3D Bluray player that output SBS, etc) since Rokid Max only recognizes at a minimum 1080p input, try using Marseille mClassic Upscaler. Works great for me. Plus, you get all the benefits of the 1080p upscaling.
https://www.amazon.com/Marseille-mClassic-Plug-Console-Upscaler/dp/B07X6KDQ98
I have two of the top ones and this thing (which is overpriced but nice to have): https://www.amazon.com/gp/product/B07X6KDQ98
Looks great on my 4K Tv.