GNOME Boxes lead developer Felipe Borges has been overhauling the application with a major rewrite and today announced the new beta release. GNOME Boxes has migrated to using the GTK4 toolkit and libadwaita. The new GNOME Boxes code can also handle installing Microsoft Windows 11 now without needing any manual workarounds for Secure Boot or TPM requirements.
The new GNOME Boxes code also introduces a VSOCK device for accessing VM contexts and other improvements. With the revamped GNOME Boxes, it's also shifting to a Flatpak-first and only model for distributing of new GNOME Boxes releases.
The main issue is that old Boxes is based on SPICE. It was/is a Red Hat project, but they stopped caring for it and deprecated it. So old Boxes is built on legacy tech that will pretty much just bit rot over time.