Backup first. Download the full Rom file. Put it in internal storage and also put there Magisk and DFE (IF YOU DON'T WANT TO BE ENCRYPTED). Boot to TWRP, flash the 11.0.8 ROM. Wipe dalkiv and cache, then don't reboot. Click the home button (if you don't want to be encrypted, flash DFE) and flash magisk.If you did the steps properly you will be able to keep TWRP, be updated to latest version and you'd have root