Here are my quick notes in order to share and remember.
There was an XiaoMi 4 phone with a broken screen and data on it.
First prepare a cable to connect the phone with the computer.
Then download the right recovery image for the phone and boot
it by switching the phone into fastboot mode (hold volume-down
button while turning on) using
fastboot boot recovery.img.
adb to connect to the shell. Oops, does
there are no connected devices? Boot with
systemd or other
udev-friendly beast which makes use of the
file (on Arch Linux installed by
adb shell do some magic with
uudecode it on the local side of the pipe and check
tar understands the data that are coming.