This fix was mainlined a couple of months after I published this. You shouldn't need to build this module by hand any more.

https://github.com/torvalds/linux/blob/master/drivers/hid/hid-xiaomi.c

Fixes Mi Silent Mouse side buttons.

$ sudo apt install build-essential linux-headers-generic dkms

(If you use a non-generic kernel, you should install the headers for that. DKMS is optional.)

$ make

$ sudo make install

$ sudo dkms add .
$ sudo dkms install hid_mimouse/1.0

$ make uninstall

$ sudo dkms remove hid_mimouse/1.0 --all