The RX protocol is specific to the reciver so for instance the model you linked to. You could buy an FRSky receiver and solder it onto the flight controllers spare UART and then configure that UART to be serial RX in betaflight.
Thats if you really wanted to downgrade the model.
personally, I’d just get yourself an ELRS radio or install an ELRS module into the JR bay of your existing radio if it supports it.
Exactly this. ELRS or crossfire the best two, flysky, FRSky etc bottom. Upgrade your tx! The radiomaster pocket looks a cool little entry level one. Though I like having the 4 in 1 module on my tx16s and then the add-on ELRS module. Means can bind to anything. Tbh only crossfire I don’t have heh