SRAM X01 Eagle 12s RD adjustment to work with 11s cassette + shifter? I want to buy:

X01 eagle 12s rear derailleur
Garbaruk 11s 10-50 cassette

I have:

GX 11 speed gripshift
KMC 11 speed chain

How do you adjust the 12s rear derailleur to the shifter and cassette? Does it automatically adjust, and you just set the high and low limits where they need to be for each cog, and the shifter just moves 11 steps in between, or is there any trick to it?
There are two things that must be correct to move the derailleur  the right distance for each shift.

Cable length pulled per shift
Derailleur actuation ratio - ratio of lateral cage movement to cable length pulled.

The 11 speed shifter will pull the correct amount of cable for the 11 speed cassette sprocket spacing through a matching 11 speed derailleur.  If the 12 speed derailleur has a different actuation ratio the cage will not move the correct distance. There is no adjustment for this.
The X01 Eagle uses what SRAM calls ‘x-actuation’ ratio, GX seems to use x-actuation and ‘exact actuation’ ratios for different components. The Exact actuation ratio is a little different and not compatible.
Check which exact model I’d grip shifters you have on the SRAM site. If they use x-actuation your proposed setup will work. If they use exact-actuation the setup will not work.