As confirmed in your topic, AAC is available and working in general, just not with this headphone (dont know why) so saying they removed it is just not correct. I understand you are frustrated about this and I dont understand your comment above at all.
“unofficial” OSes can often implement things easier as they dont need Google or Qualcomm Certification and approval.
Edit: statement from FP2 LOS developer, so are you sure its implemented on the FP3 LOS, any proof you can link to?