For anyone encountering this in the future, you can mount the a steam deck formatted filesystem by toggling casefold off via this command:
sudo tune2fs -O^casefold <partition label, e.g. /dev/sdf1>
Once you are done, unmount the filesystem and run this command to revert the change:
sudo tune2fs -O casefold <partition label, e.g. /dev/sdf1>