Have you tried the installation without formatting data? I did and it worked for me. A factory reset should be enough to install it.
You said after the installation there's nothing. Is the device booting to twrp or is there anything else happening?
IIRC my device booted twice after the installation but came up with the setup process after that.
Maybe try flashing the zip file and install magisk 16.7 right after that without rebooting to system. Did the trick for me on some other GSI roms.
Magisk doesn´t make anything better...if anything then worse.
REdownload the files and flash again. Just had that same problem som days ago with my LeEco....Update downloaded flashed....and NOTHING.
Corrupt downloads as it turned out once again.
The fileservers the ROMs often are stored at at not the best....but I understand....they are for free