I followed this instructions for the Armor 6 from @Extosis and it worked with a few changes of course!
My changes and notes:
1- I downloaded the Armor 7 ROM from ulefone / support/ software-download (my armor was version dec-31-2019). I'm on the NonEU version.
2- Magisk 20.3 and Magisk Manager 7.5.1
3- I did my backup (photos, videos, custom launcher and other apks) to an USB stick for later easy re-installation instead of an adb pull
4- If it is the first time that your PC and Armor are connecting through adb, you might need to grant permissions in a phone dialog
Hope this helps!