Automatic update is a form a malware. It makes changes to your system without your knowledge or consent. Even if all you think it’s doing is making “fixes” to “bugs”, users’ code may well have work-arounds or even depend on those “bugs” to produce the specific output they want.
Any installation method for Processing should allow for multiple installed versions, letting users test new versions on their old code before fully committing to a switch, and/or should allow an easy roll-back to an older version.
Snap is a proprietary format under control of a private company and many Linux distributions refuse to work with it. If you want to support the widest range of Linux users, please still provide .tar.gz files with the same install script that Processing has had for years. The install script worked well, supported multiple version installs, and made it easy to switch between them. And include the Processing version in the directory path so that new versions don’t overwrite existing ones.
Please add the portable version installer or the .tar.gz versions to the Processing download web page and make it obvious that your current “download” link is a forward to Canonical’s Snap store.