I never backport anything with the RPi kernels. The kernels are unchanged from what RPi provides. You start changing up their kernels and they stop talking to you when there are issues.
I will though occasionally temporarily patch the kernel with a fix if there is one available to fix a know issue until it gets fixed in the kernel if it is not something RPi is responsible for. Other wise I open an issue with RPi.
I recompiled the linux-rpi5-mainline-6.15.6-2 kernel with bluez patch they came up with. Download and unpack artifacts.zip and install and test to see if it fixes your issue. If it does I will apply the patch to all pi kernels until upstream fixes the issue starting with the next kernel upgrades.
https://gitlab.manjaro.org/manjaro-arm/packages/core/linux-rpi5-mainline/-/jobs/15930