What is AEA/DT?

It's a stabilization end date. That one is for KD time. Units usually put it on prior to Training Center rotation but it can be applied other times as well. Before an NTC/JRTC rotation you'll see a lot of "D" and "F" AEA codes applied to key leaders. "D" is KD and "F" is Crew Stabilization. The end date means you can be placed on assignment but your report date can't be before Feb 2022

Looks to be AIT Platoon Sgt Stabilization. AEA codes are assignment restrictions, basically saying you can't get PCS orders until the date your code expires

Doing some googling, it looks like you are in an HRC holding pattern for either Drill Sergeant or Recruiting. I found an old RP post mirroring your question. Here is the link.
https://www.rallypoint.com/answers/what-does-an-aea-dt-code-of-t-201902-mean