I want to create a new subfolder called Example, and inside I will have a Settings link. So in the Admin toolbar should be Configuration > Example > Settings. My example.links.menu.yml looks like this:
example.admin: title: 'Example1 settings' description: 'Settings for Example' parent: system.admin_config_system route_name: example.settings
Let's say example.settings exists. I think it should be something like this
example.admin: title: 'Example1 settings' description: 'Settings for Example' parent: system.admin_config_system/example route_name: example.settings
Note that inside Admin > Configuration > Example there will be more links from different modules.