NOTE: I won't be updating this in future, I decided that I didn't understand it enough and there were still issues. I have created a new plugin that also supports TAXONOMIES at: https://wordpress.org/plugins/extend-revisions-for-custom-fields-and-taxonomies/
Enables custom fields in revisions and allows to restore them.
- Upload the PHP file to the "/wp-content/plugins/custom-fields-revisions" directory.
- Activate the plugin through the 'Plugins' menu in WordPress
- [Dennis Bareis] Modified to work on WP 6.2 & PHP 4.7