My E5 came on 8.0 Oreo.. but you can't decrypt the factory ROM.. You have to flash a custom ROM.. I was able to flash a Custom ROM, and disable the encryption. But, you need a SD Card with the files on it already. I don't know if this will work for you, but it worked for me.
What I did was download the TWRP 64-bit recovery that is in this thread, Pixel Experience ROM, and Magisk 19.3 to my SD Card while on PC . I also downloaded this TWRP flashable Disable Encryption command ([yadi.sk/d/HLr5vjnkA8gaqw )
Put TWRP in the same folder as your ADB and Fastboot root. I also renamed the TWRP file to something simple to run for the command (IE hannah.img) and did everything like this in the terminal, and on the phone like this..
adb reboot bootloader
fastboot flash recovery hannah.img
fastboot boot hannah.img
The phone should reboot into the TWRP recovery. Once it boots into TWRP you can back up the stock ROM to the SD Card. Then go to WIPE, FORMAT DATA, YES. Once the format data is complete. Go to Reboot, and hit Recovery. This will reload TWRP again. Then, you can go to INSTALL, go to your SD Card, and Install the ROM you chose, GAPPS, Magisk 19.3, and the Disable Encryption zip.
After everything installs, do not reboot from the completion menu. Go back to the main menu of TWRP, and hit the REBOOT option, go to Bootloader. And, select START from there. The phone will go blank with N/A in the top left corner for a while. Just give it time, but then you should see the splash screen for whatever ROM you're using. Just give it time, and it will eventually boot up.
That's what worked for me.
what android version you on?