If you feel desperate and you’re sure it’s a diskspace issue and you do have backups - you can delete directories via fbe when unencrypted too, you just don’t know what you’re deleting.
mount userdata via
mkdir -p /mnt/userdata
mount /dev/block/bootdevice/by-name/userdata /mnt/userdata/
du -cs /mnt/userdata/* | sort -n | tail -n10
and go rummaging?
an aside: mounting + chrooting /system and /lib partition (for shared lib dependencies) one can use vold for volume management - and maybe it has cli options to do the decryption for the ext4crypt scheme interactively. You can also push binaries (openrecoveryscript) via adb to the device… but really do that exploring only if you can stomach losing the userdata