I am having a hard time pairing my new Airpods pro to my laptop (Thinkpad P15-Gen-1 running Ubuntu 20.04 LTS). I did the editing of sudo nano /etc/bluetooth/main.conf to set ControllerMode = bredr as many other posts have suggested. When I run journalctl -f, I see that I get the following message when I try to pair my Airpods:

Setting up /org/bluez/hci0/dev_XX_XX_XX_XX_XX_XX failed: GDBus.Error:org.bluez.Error.AuthenticationRejected: Authentication Rejected

Can anyone tell me why I am getting this message and how I may solve the problem?

EDIT: Well I solved the problem - I did the factory reset per Apple's instructions, and it works well on Linux Kernel 5.10 (I was previously booting into 5.8 which was the default, but then I purged and unsuccessfully tried to re-install bluetooth controller).

I wanted this to be a learning experience, so I will give the bounty to a poster who can explain what goes on when I reset a bluetooth device.

EDIT V2: @Raffles, sorry for the late response. Here is the output of dmesg | grep tooth

[    2.553762] Bluetooth: Core ver 2.22
[    2.553775] Bluetooth: HCI device and connection manager initialized
[    2.553777] Bluetooth: HCI socket layer initialized
[    2.553779] Bluetooth: L2CAP socket layer initialized
[    2.553781] Bluetooth: SCO socket layer initialized
[    2.569503] Bluetooth: hci0: Bootloader revision 0.4 build 0 week 30 2018
[    2.570510] Bluetooth: hci0: Device revision is 2
[    2.570511] Bluetooth: hci0: Secure boot is enabled
[    2.570512] Bluetooth: hci0: OTP lock is enabled
[    2.570512] Bluetooth: hci0: API lock is enabled
[    2.570513] Bluetooth: hci0: Debug lock is disabled
[    2.570514] Bluetooth: hci0: Minimum firmware build 1 week 10 2014
[    2.573522] Bluetooth: hci0: Found device firmware: intel/ibt-19-0-4.sfi
[    2.576644] thinkpad_acpi: rfkill switch tpacpi_bluetooth_sw: radio is unblocked
[    4.414524] Bluetooth: hci0: Waiting for firmware download to complete
[    4.415490] Bluetooth: hci0: Firmware loaded in 1803652 usecs
[    4.415525] Bluetooth: hci0: Waiting for device to boot
[    4.430511] Bluetooth: hci0: Device booted in 14643 usecs
[    4.430700] Bluetooth: hci0: Found Intel DDC parameters: intel/ibt-19-0-4.ddc
[    4.432526] Bluetooth: hci0: Applying Intel DDC parameters completed
[    4.433495] Bluetooth: hci0: Firmware revision 0.0 build 121 week 36 2020
[    5.743112] Bluetooth: BNEP (Ethernet Emulation) ver 1.3
[    5.743113] Bluetooth: BNEP filters: protocol multicast
[    5.743116] Bluetooth: BNEP socket layer initialized
[    5.773904] Bluetooth: RFCOMM TTY layer initialized
[    5.773909] Bluetooth: RFCOMM socket layer initialized
[    5.773913] Bluetooth: RFCOMM ver 1.11