I have successfully compiled and created 3 PET packages of Emacs 28.1 on a Bionic64-8. Runs well as far as I can tell. I could do it for Fossapup64 if this one doesn't work or there is an interest.
Download the PET file(s) and click on it, let it install. There should be .desktop
files available in /usr/share/appplications
This package has not been tested at all yet. Use at your own risk.
emacs-28.1-x86_64.pet
emacs_DEV-28.1-x86_64.pet
emacs_DOC-28.1-x86_64.pet