Bummer on the Stages issue…I just ordered the Stages for my GRX, and am definitely looking forward to it. Haven’t even got it back yet. I think that’s the best, and maybe the only option. 4iii’s power doesn’t have an option available, yet.
So, I think it is SRM who is making an SPD style power pedal, and that would be rad. You could also get Garmin Vector, or Power Tap pedals and just use a pair of road shoes and cleats. I use mostly road cleats and pedals on my Gravel bike for long rides. Very light and smooth over long efforts. The only real reason you need SPD’s is for lots of on and off with hiking and mud/sand. Most true gravel rides have very little need for SPD.
The other option would be to go to an old school Power Tap hub. I think you can find someone getting rid of one fairly cheap.
I imagine 4iii will come out with something soon. Or, ship your non drive side crank arm to a buddy in the States, and have him send it to Stages.