No Planner Desktop App is Available
Some wonder why Microsoft never developed a Planner desktop app. It’s probably due to a lack of engineering and support resources. But a good workaround exists because you can create a desktop app from the tasks.microsoft.com web site. For guest access to Planner in another tenant, a desktop shortcut might work. And there’s always the Tasks by Planner app in Teams. So maybe a Planner desktop app isn’t needed.