Thanks for updating. You can try on of the suggested plugin if you can’t get it work by editing on Child Theme. If the plugin doesn’t work on preview then you might facing cache issue. Let’s try deactivating cache plugin if you have any.
For some reason, at least in my case, the previous plugins didn’t change the order for the query, only for the visual aspect in the panel.
The plugin Post Types Order did though! So now it works as it should 🙂