Sadly you sort of make my point for me...
http://www.bluez.org has release notes, downloads.... but not much documentation. The best they have is a link to the study guides on bluetooth.com
https://www.bluetooth.com/bluetooth-...es=study-guide
The debian link is mostly a page of broken links to elsewhen.
The archlinux is one of the better ones, but not a reference doc... alas, the whole ecosystem seems to be in a state of transition, with some important tools deprecated without being replaced.
https://wiki.archlinux.org/title/blu...ed_BlueZ_tools