How to get touchscreen on M1 Macbook Air

I know, i know macOS doesent support touchscreen but i NEED a external monitor that has touchscreen and works with mac. Ive seen it done before but dont understand how they do it. I saw a idea where a monitor would have a mouse emulator built in but i cant find any. My budget is 200$ so let me know what idea you guys have and how to do it.