Disable auto save functionality at all.

Easiest way is to use a plugin: https://wordpress.org/plugins/disable-gutenberg-autosave/

Let me know if that works — otherwise, I can see about finding another approach to disable it.

There isn’t much difference between using a plugin and writing the code yourself. But, it sounds like this might work?

define('AUTOSAVE_INTERVAL', 86400);

86400 is a day.

Hmm, in that case, you might want to look at how the above plugin does it and try out some of their code.