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.

Then use adb to connect to the shell. Oops, does adb say there are no connected devices? Boot with systemd or other udev-friendly beast which makes use of the android.rules file (on Arch Linux installed by android-udev package).

By using adb shell do some magic with tar and uuencode. Then uudecode it on the local side of the pipe and check the local tar understands the data that are coming.