Try Mark Jaquith’s Menu Humilty Plugin: https://wordpress.org/plugins/menu-humility/
That plugin is almost what I’m looking for. It moves all the annoying top-level plugin menu items down to the bottom. Which does get them out of the way at least a little bit. I would still prefer them to be sub-menus though.
There may be a plugin that is closer to what you’re looking for – you may have to try a few, but I expect you could find some to investigate if you search the plugins director with relevant keywords eg:
https://en-gb.wordpress.org/plugins/search.php?q=admin+menu
Thanks to cubecolour I found one that works! It allows you to move around menu entries wherever you please. Although it requires you to make another entry for a submenu item, it still works!
https://en-gb.wordpress.org/plugins/admin-menu-editor/
Thank you!
Can a sub menu item have a sub menu item listed under it? I only see Top Level and Sub Level.