We're planning to release b3 in a few weeks, but I'm afraid it's going to take longer than that before Xway can read Freeway documents.
New features in b3 include the ability to import Exhibeo galleries, and full support for copy and paste.
I'm still using Mojave, but I will probably upgrade to Big Sur when it's released (and Apple have fixed any serious bugs). My plan for then is to install Mojave within a virtual machine (VMWare or Parallels Desktop). There is a TidBITs article that explains how to do this:
If you decide to do this, download the Mojave installer from Apple before you upgrade (it's difficult to download it after you've upgraded).