I am uncertain about this. I believe this is started during any GUI login. Some GUI login control via systemctl is non-standard in L4T, although I couldn’t say exactly how. The gist is that using systemctl to disable a GUI login is different than the steps required to do so on a PC Ubuntu. I suspect what you are running into could be part of that if systemctl cannot do a normal disable.
If nobody is logged in to the GUI, and you have used a serial console or ssh login (or CTRL-ALT-F2), what does this do?
sudo systemctl disable avahi-daemon.service
sudo systemctl list-unit-files | grep -i avahi
You may find this of interest since I believe it is the GUI running which triggers the restart even after a disable:
…basically it says to “sudo systemctl mask avahi-daemon.service” instead of disable. Only auto start goes away upon disable…mask actually bans.