Fix retropie 4.7.1 + 8bitdo bluetooth

https://retropie.org.uk/forum/topic/29996/issue-connecting-bluetooth-8bitdo-sn30-pro-controller/5

THE FIX:
You need to exit RetroPie settings (go back to the Emulation Station menu) and the exit Emulation Station by pressing F4. This will take you back to the console.

From there, run this command to edit a file:

sudo nano /lib/systemd/system/bluetooth.service
Replace

ExecStart=/usr/lib/bluetooth/bluetoothd
With (the # character will disable old the configuration, then add the new underneath)

#ExecStart=/usr/lib/bluetooth/bluetoothd
ExecStart=/usr/lib/bluetooth/bluetoothd --noplugin=sap
This disables the problematic plugin.

Then open this file for editing:

sudo nano /lib/systemd/system/bthelper@.service
Replace

[Service]
Type=simple
ExecStart=/usr/bin/bthelper %I
With (the # characters will disable the old configurations, then add the new underneath)

#[Service]
#Type=simple
#ExecStart=/usr/bin/bthelper %I

[Service]
Type=simple
ExecStartPre=/bin/sleep 2
ExecStart=/usr/bin/bthelper %I
ExecStartPost=sudo /etc/init.d/bluetooth restart
After rebooting, sudo bluetoothctl works as expected with pair, trust, and connect for the Bluetooth devices we have tested (mostly 8BitDo controllers).

DON'T FORGET TO SET THE UDEV RULE
https://retropie.org.uk/docs/8Bitdo-Controller/#firmware-versions-for-8bitdo-controllers