SRAM GX Eagle AXS 12-Speed 52 Teeth Long Cage Rear Derailleur – Lunar
Here’s my used electronic GX AXS derailer from a couple years ago still works great I just upgraded to XX1. No battery, got a few scratches on it from regular use but works great. Sold as is free shipping. 
SRAM GX Eagle AXS 12-Speed 52 Teeth Long Cage Rear Derailleur – Lunar
SRAM GX Eagle AXS Rear Derailleur – 12-Speed, Long Cage, 52t Max, Lunar
Engineered with a variety of rider preferences in mind, it is compatible with the expanded range 10-52t cassette as well as the 10-50t cassette. Every bike we list is owned, inspected, and held by us; we donât consign or list for others.