To switch back to classic mode, you need to install and activate the Classic Editor plugin.
I also like it more than Gutenberg. I don’t even see a feature in Gutenberg that would show how many words long my posts are, which is an important metric.
On the subject of autosave, it would be helpful to have an option to set it manually to turn it on, off or 5 minutes, etc. Lacking that feature you can do this easily. Just add following line to your wp-config.php file:
define(‘AUTOSAVE_INTERVAL’, 86400);
86400 is a full day, so you may want to set it to a smaller number.