I gave too much detail last time.....12 speed rear deraill on 10 speed gear?
 

Will a 12 speed SRAM GX rear derailleur work with a 10 speed GX cassette, chain, and shifter?

I'm thinking of going 1x12 eventually but I'll have to save up some more pennies and need a new derailleur now.

Thanks!

No. In the MTB range, SRAM switched from "Exact Actuation" to "X-actuation" for 11 speed and above. Your 10 speed GX shifter is "Exact Actuation" and the 12 speed GX derailleur is "X-actuation", which means they have different cable pulls.

I did not know that! Thank you for the answer!!!! Now I want to ask you what it would take to make my current wheel work with a 12 speed cassette??? I'm on a handbike cause I like to make things trickier than they should be.....oh, and cause my legs don't work.

The Sunrace MZ90 12 speed cassette will work on any Shimano/SRAM compatible 8/9/10 speed freehub body.

The least expensive route is probably the Sunrace cassette, and SRAM NX Eagle shifter, rear derailleur and chain. The 12 speed chain should work fine on your 10 speed chainring, since the inner width of the chain is the same.

Thank you!!!