Something like this then?
https://www.amazon.com/Modulator-Converter-Demodulator-Composite-Component/dp/B0976L5C7B
Digital, as in digital television? then you need a DTV converter box:
https://www.amazon.com/dp/B096N6PBWP/
Digital, as an HDMI signal? then you need a HDMI to RF converter box:
I leave my PC resolution on at 1080p and mine converts it by itself. Works a hell of a lot better than my cable box.