On my laptop I use a Bluetooth keyboard and a Bluetooth mouse. Occasionally the Bluetooth adapter in the laptop shuts off completely, which means that it is not even possible to restart the Bluetooth service with
sudo systemctl restart bluetooth.service.
My troubleshooting points to powersaving as the cause of this, but the TLP setting that is supposed to prevent autosuspend on Bluetooth devices does not seem to prevent this sudden death of the Bluetooth connection. As a temporary workaround I am using the commands below to restart Bluetooth from the shell.
$ sudo rmmod btusb && sudo modprobe btusb && sudo systemctl restart bluetooth.service
This solution works on Debian testing bullseye with kernel x86_64 Linux 5.5.0-2-amd64.