Hey all! I wrote this post, based on some personal notes from a personal project I worked on a few months ago. I hope you don't mind the self-promotion; I get nothing out of it other than knowledge sharing.
It's not a fully comprehensive post on BLE GATT reversing, but I hope there's enough content to get you started on the matter.
The post is a little rushed (I don't have much free time nowadays), so please feel free to let me know about any potential inaccuracies you find.
Further posts may follow, adding more details on this project or reversing more hardened targets.