If you have a standard Apple PKG and simply want to wrap its contents into an ISO for archiving or cross-platform use:
If your .pkg file is actually a installer application ( .app wrapped in .pkg ), then you might directly use it. how to convert pkg to iso exclusive
Converting a (macOS Installer Package) to an ISO is typically done to create bootable installers for virtual machines or recovery drives. Because a PKG is a compressed installer, you must first extract the application before converting it to a disk image. Recommended Method: Using Terminal (macOS) If you have a standard Apple PKG and
Some PKG games are compiled as "retail" or "HDD" versions. You may need to resign the EBOOT.BIN file to a "disc" format to ensure compatibility after conversion. Step 3: Rebuild as ISO Recommended Method: Using Terminal (macOS) Some PKG games
Converting PS3 PKGs to ISOs is "hit or miss" because many PKG files are designed as installers rather than disc images. How to Convert macOS Monterey Installer to an ISO File!