The community support and platform support are for widgets/modules in the appstore.
So if you use a widget from the appstore and mendix has stated it as Platform support you can send a ticket to mendix support when you have issues with this particular appstore widget/module.
Community support just means that the appstore item has not recognized by mendix as something they should support as a first party. But usually you can just reach out to the developer who made the widget/module for any issues. Either through the community page or their github page.
If you need support with the Mendix platform you can always reach out to mendix through their support page.
Then again, if it’s about functionality you as a developer/consultant or something built. Then you are the point of contact/‘servicedesk’ for your client.