Ok, consider the case the root filesystem was compressed using squashfs or erofs into a file called rootfs.erofs.

According to this, I think booster should check whether the root filesystem is compressed/squashed or not, if it is then an additional mount command should be run:

...
mount -t erofs -o ro /dev/some_loop_device /some_mount_directory
...

So in addition to checking for /dev/sr0 and mounting it, booster should also check whether another parameter is passed that specifies the location of the root filesystem on /dev/sr0 whether it was compressed or not (for example another root= as an argument for booster and not for cmdline)..