Hmm let me remember...
Go to Vendor/etc …> fstab.xxxx open it and go to data line, at the end of the line you'll see the encryption, just delete it (same as image) the word "check" is the latest word that needs to be keeped.
Now go to recovery.fstab and do the same look for userdata and delete the encryption part until length=xxxx.
Look at the pictures that I attached.
After that reboot and do the wipes on stock recovery. Now try Twrp

it worked for me.
Don't waste your time if you are going to use OpenKirin roms, because it didn't worked, it encrypts again the device. I have an idea about which file I need to edit but I haven't tried it yet, because I'm using Aosip.
Hope it works for you