I am looking to build an app that will live on the taskbar but needs to have an extended size (i.e. not just be a square icon). I know that these types of apps are extremely uncommon in the Windows world, but nonetheless, the search box on the taskbar in Windows 10/11 is the closest to what I need.
What API(s) does that search app use?
Is there another app out there (ideally open source) that does something similar?
Up to Windows 7, apps can implement custom Deskbands directly on the Taskbar. However, that feature is deprecated after Windows 7 (also see Is it possible to add a DeskBand (or similar) to the Notification Area in Win 10/11?).
Going forward, Microsoft wants apps to use Thumbnail/Live Previews and Thumbnail Toolbars instead.