Last week, I gave an old laptop a second life. It's an old ASUS, I think it came with Windows 8 back in the day, and I installed Debian 11 with XFCE on it. This looks very retro, but it works like a charm. I can now use the battery for serveral hours, while with Windows it would die after 5 minutes. And today I got my bluetooth mouse working.

Here is what I did:

apt install blueman
apt install bluez-firmware # not sure this was actually needed
apt install bluez-tools # update 2023-09-06: This is actually needed

With blueman installed, the menu under 'Applications', 'Settings' now contains an item 'Bluetooth Manager'. The problem was that it discovered all kinds of bluetooth devices, but not my mouse 🙃

To solve that, I also had to

modprobe uhid

(Thank you, Stack Exchange).

So I added uhid to /etc/modules, to make it load at boot time.

Update 2023-02-14: After I had used the mouse on an other device, it didn't show up anymore in the Bluetooth Manager. I got it working again by running

bt-adapter -d

in a terminal.