You need DJI goggles to use the DJI air unit (or the Caddx Vista/Runcam Link). The digital stuff is all proprietary.
If you don't want to buy a digital FPV system, I'd recommend going with the cheapest set of box goggles you can find. These are about \$50 with an analogue camera and VTX being about another \$50. It's not a bad idea to start with analogue gear, in case you lose the drone entirely or otherwise damage it.
Box goggles are a bit chunky to transport and wear, but the picture quality is pretty similar to much more expensive goggles. It doesn't really matter how good the screen is when the input signal is low-quality.
Most importantly, once you see the view through digital HD goggles, you will want to start saving for it. The record in our club is under a week from trying it to buying it.
One way to save money is to buy second hand DJI goggles. Now the third version has been released, some people are selling their earlier versions.