The released LaTeXML snap package is located at Snapcraft: LaTeXML snap.
If you are on macOS you can install snap to any of your multipass instances with:
multipass transfer latexml_*_amd64.snap ${instance-name}:/home/multipass
multipass shell ${instance-name}
sudo snap install --devmode latexml_*_amd64.snap
After this the snap is ready to use.