I want to install LineageOS and GrapeneOS on VirtualBox, but they are not all iso files but zip files. I want to install a zip file OS on Virtualbox. How can I do that?
Take a look at Android-x86 (https://www.android-x86.org/). They provide iso files.
You cannot. LineageOS and GrapheneOS are ARM-based Android ROMs, not x86-based operating systems your computer and VirtualBox are expecting.
Android-x86 like @infosechandbook mentioned is the only Android OS you can install in VirtualBox, not Lineage or Graphene.
How can I install LineageOS or GrapheneOS?
With GrapheneOS, a Pixel 2 at least. With LineageOS, a OnePlus will do fine.
Did somebody try out Android-x86?
I tried it many years ago and it was quite unusable. Still the case?