It's not supported on Windows 11, as of this writing.
Here's the Microsoft's official response on the Feedback hub about this:
Currently, dragging a file onto an app in the taskbar to open it in that app is not supported in Windows 11, but we appreciate all your feedback, and we’ll continue to use it to help guide the future of features like this.
You can upvote the feedback (
https://aka.ms/AAd4ejq) to get this feature back.
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