What is H&F's thought on this?

I've been considering changing my cardio days to 15-20 minutes HIIT (30 seconds on/off 90MHR/70MHR, 2 min warmup/cooldown) followed by 20-30 minutes of SS moderate cardio (70% MHR).

As for what cardio, I'm considering a pair each day choosing from: Cycling, Elliptical, Incline Treadmill.

Or you could focus on your kcal expenditure and intake to decide your fat loss
and supplement with cardio when you see fit
no need for that excessive amount. Just do one or the other. I'd do mainly HIIT because it's much better in most all aspects but it can become burdensome on the CNS if done excessively overtime, as well as amplifying glycogen depletion, esp during prolonged dieting, then that's where LISS can come in handy.

During a cut IMO you should only add cardio to keep nutrient intake high while keeping a deficient.
I would rework your macros if I was you.

I eat at a big kcal deficit but my weight has been the exact same for about 18 months.

Probably not counting your calories correctly, or you overestimated how much you really need.

If you must, LISS is my opinion.

hiit before your workout will definitely bring your workout down

and you should do some form of cardio 3-5x a week for your health anyway, just don't have to over do it

Your metabolism is probably rekt m8 gl rip

Yeah, I believe it is. Been eating at a deficit for so long it's probably destroyed. Oh well, RIP in pieces Ryan's metabolism.

fuck cardio. calorie deficit all day everyday.