https://www.mtbr.com/threads/3-13-solution-for-sram-eagle-axs-derailleur-noise.1214185
There are a few ways of doing it. An o-ring, but people say it shreds over time. An M10 x 16mm OD x 1mm thick aluminum washer. Or wrap some plumber's tape around the bolt head so it acts like an oring. Or you...
I have the sram GX AXS derailleur on my levo (non t-type). The derailleur is loose and floppy due to design, makes the bike noisy on rough downhills. I added some plumber's tape to the derailleur bolt as per suggestions on another MTB forum. It tightens up the derailleur a bit so it doesn't flop...