Pair Bose QuietComfort 35 with Ubuntu over Bluetooth

This project is aiming to resolve problems that you can encounter when pairing your headphone.

1) Get back to a clean state

On Ubuntu, remove the headphones from the Bluetooth paired list.
On the headphones, hold the switch in Bluetooth pairing position for 10 seconds to delete all paired devices (You'll get a voice confirmation).

Edit bluetooth configuration file:

sudo nano /etc/bluetooth/main.conf

Replace the following (remove the "#" symbol at beginning of the line if it exist):

ControllerMode = dual

With:

ControllerMode = bredr

Restart bluetooth service:

sudo service bluetooth restart

Edit or create this file:

sudo nano /var/lib/gdm3/.config/pulse/client.conf

Insert these following lines in this file:

autospawn = no
daemon-binary = /bin/true

Grant access to GDM user:

sudo chown gdm:gdm /var/lib/gdm3/.config/pulse/client.conf

Disable pulseaudio startup:

sudo rm /var/lib/gdm3/.config/systemd/user/sockets.target.wants/pulseaudio.socket

For Auto-connect A2DP, edit this file:

sudo nano /etc/pulse/default.pa

Insert following lines at the end:

.ifexists module-switch-on-connect.so
	load-module module-switch-on-connect
.endif

After saving these changes, you must reboot now.

via package manager:

sudo apt install blueman

To pair your headphone:

If you want to reverse this configuration, you just need to follow steps in reverse order.

Note: Thanks to issue #2, I have added to the repository pulseaudio.socket file which is removed at the end of step 3.