um I think you are missing a step. From theh community plugins window you click an X next to the enable or disable slider to uninstall a plugin. Then you should get the pop up as described by the poster above. On thatPop up you must click the UNINSTALL button not the X.
X in the popup is a cancel and will not do the uninstall. It’s a backup in case you clicked uninstall by accident and have decided not to uninstall the plugin.
Maybe I’m misunderstanding your problem?