Can dual boot Mac access files between two OS installs I have a High Sierra Mac, I was thinking about doing a dual boot setup with Mojave or Catalina.

Will I be able to copy files between two installations via Finder?

Or another way to ask, when I am running the newer OS, will I be able to access files on the older OS in Finder without copying them to an external drive first?  Vice versa?
What I found by installing Catalina in a new partition on the High Sierra disk is that:

When logged in to Catalina, the High Sierra disk appears as a drive in Finder.

When logged in to High Sierra, the Catalina disk can be available but Finder will ask for a Catalina User Name and Password to access it.