OpenWrt x86 SquashFS and disk space

Installing and Using OpenWrt
1

Hello
Is it possible to use the none ext4 image i.e. SquashFS version of an x86 image and create an overlay image with the rest of the space on the disk?

I have a 120GB built-in flash storage and my custom-built OpenWrt is 512MB. I would prefer to use the squashfs version so that I can do a factory reset.

2

https://openwrt.org/docs/guide-user/additional-software/extroot_configuration ?

3

Adding free mounts is more manageable, like sysupgrade etc