As Ubuntu 20.04 did not include the package, sane-airscan, it will be incredibly difficult to get it to work. My Brother HL-L2390DW has the same story. I've tried everything suggested in this thread and nothing has worked.
I've even tried installing sane-airscan separately as a deb, but it lacks up to date drivers.
The good news is Ubuntu began including sane-airscan in 20.10. With this package, most Brother scanners work fine. With the 22.04 LT release later this year, Brother-help is on the way.
fyi- Only Linux distros still lagging behind with the 20.04 Ubuntu support don't work on my Brother. Every other distro I 've tried - it works.