Most Functions Gone

When you say items what do you mean? plugins?
If so, likely a plugin is causing this issue.
Try deactivating all plugins and the activiting one at a time.

https://www.wpbeginner.com/plugins/how-to-deactivate-all-plugins-when-not-able-to-access-wp-admin/

Let’s just say I lost the ability to edit my products and change the appearance of my site.

I’m quite sure there’re others though

Ok well this forum is for general WP issues and if you are have lost the ability to edit products, then this would be a plugin issue.

Please contact the plugin author.