Unable to mount overlay on openwrt x86

Hello guys,

I recently replaced my hardware router with a Celeron board. A modified openwrt x86 is installed on a 32GB USB drive.

Aside from the firmware partitions, I divided the rest space into 2 partitions and planned to use the first one as overlay.

Here are the partitions.
sda5 is the one for overlay which is in f2fs.

Here is the setting in fstab

config mount
	option enabled '1'
	option device '/dev/sda5'
	option target '/overlay'
	option fstype 'f2fs'

But after startup, this is what I see with df -h. /dev/sda5 is not mounted.

If I manually mount the partition or put mount /dev/sda5 /overlay in rc.local, this is what I get
the partition is shown as an image not in overlay. New packages, etc, will still be installed in the system partition. findmnt command gives information like this
which appears /dev/sda5 is mounted correctly.

What is wrong with this?