One approach is to buy a smart TV and remove the controller board. Get a new control board (sometimes called a scaler, since that's its main function) with only the functions you need. These are available mostly on aliexpress, if you punch in the display panel part number and the word "board". Expect to pay about $90-150 for a 4k board.

This isn't the best option, and it's a giant pain in the ass, but it's very effective.