avd manager – Which format the system images for avd are in

After downloading an image for android virtual device via avdmanager there are system.img userdata.img ramdisk.img and kernel_ranchu in system images folder. Which format are they in and how to read/mount them outside avd?

My investigation so far:

As many people here and over the internet suggests they are sparse images. But they are nit. Simg2img hence doesn’t work.
System.img is not a raw ext4 image either.

file ststem.imgreturns dos/mbr boot sector. With fdisk -l there are 2 partitions in the gpt partitioned image, labeled as linux partition.But setting up losetup none can be mounted. Even file -s doesn’t recognize partitions. Interestingly first partition os from offset 2048 to 4096. Second is the rest.
These images are definitely not encrypted as strings returns readable data like app names script contents.

So I’m wondering what kind of filesystem that can be.

Ps: the sw apply for both google play and aosp devices.