This lack was already there before on devices where TWRP doesn’t support decryption of user data …
Backing up Internal Storage seems tricky, so TWRP leaves that out by default … https://twrp.me/faq/backupexclusions.html. TWRP backups by default were never complete.
Adding to that, the user data partition in recent Android is mandatorily encrypted, getting decryption to work in TWRP is tricky, so TWRP leaves this to individual device maintainers to support, or not … https://twrp.me/faq/encryptionsupport.html.
Something is coming to /e/OS supposedly regarding backup …
Since /e/OS supports Rooted debugging (which isn’t rooting the device, but only gives root to ADB), you could have a look at solutions able to use this, like perhaps
As a user, you can always copy Internal Storage via USB or other means, and you can always reinstall the OS by keeping the install files and tools.
With rooted ADB you should be able to access the part of the data partition you normally as a user can’t cover with a backup.