1. How to Install:

   sudo apt update
   sudo apt install fuse libfuse-dev libicu-dev bzip2 libbz2-dev cmake git libattr1-dev zlib1g-dev g++
   sudo snap install cmake --classic
   
   git clone https://github.com/sgan81/apfs-fuse.git
   cd apfs-fuse
   git submodule init
   git submodule update
   
   mkdir build
   cd build
   cmake ..
   ccmake .
   # Choose fuse3 off -> c -> g -> q
   make
   sudo make install
   

2. Unzip *.ipsw: ipsw is a zip file.

   7z x iPhone_4.7_P3_14.4_18D52_Restore.ipsw
   

   You will have 10 files or so. The biggest dmg file is a file system image, which can be mounted by apfs-fuse.
3. mount the dmg file.

     apfs-fuse 038-96130-062.dmg /mnt
     umount /mnt  # after you use it.
   

the dmg file could be mounted and seen in the file system. But reading contents of files was failed.