I have seen these error messages many times. Follow the steps below exactly:
Reboot into TWRP recovery
Now tap **Factory Reset**, then **Format data / factory reset** and continue with the formatting process. This will remove encryption and delete all files stored in the internal storage, as well as format your cache partition.
Reboot into TWRP recovery again
To be on the safe side and for testing, clear again:
Wipe > Advanced Wipe >Dalvik/ART Cache, Cache, System and Data.
Repeat the deletion until no more error messages are displayed.
Return to the main menu.
Tap > Mount and
check¹ whether the /data partition can be activated.
¹Only check, do nothing else
If the /data partition is ready to be mounted, continue with the installation of the /e/OS ROM …
Now the eOS ROM is flashed by tapping the TWRP button “**Install**”, selecting the file e-0.13-o-2020120889191-dev-herolte.zip from your **microSD** card and installing it. At the end of the automatic installation process, tap Wipe > Dalvik/ART cache and boot into the SYSTEM.