Too bad in this case, otherwise a more safe setting as said.
Don’t bother researching unlocking it now. If even successful, locking as well as unlocking the bootloader will force a factory reset for security reasons, wiping user data.
(For others finding this topic with the issue of full storage …
With an unlocked bootloader you could boot the alternative TWRP recovery without installing it, and even if TWRP perhaps wouldn’t support decryption of the encrypted Internal Storage, you could still use its file manager and terminal to possibly access Internal Storage in encrypted form. Because halfway recent Android uses file-based encryption, you would see garbled folder names and file names in there, but file size should be visible for making guesses to blindly delete large videos or downloads and such to get the storage operational again.)