Something that just has a perfect fit and full transparency. Something that is only done on Open Source Operating Systems.
OpenBSD can be seen as perfect because the code base is very strict and securely written. Making it a nearly bug free OS. But I never used it.
Linux Distros that have a large repository to install apps from can be seen as perfect because you cant create a chaos where you dont know how to uninstall things, as everything is installed through the same package manager. Satisfying for updating too. Something like NixOS, Gentoo or Arch.
I dont see them as the “perfect” but Windows… even debloated. Its still a huge chaos.