Display image when no message is selected

[Carnotaurus]

This is something that is just cosmetic, but coming from the now defunct Mail and Calendar app in Windows 10/11, I liked how that app could display a graphic of the user's choice in the reading pane when starting up, and when no message was selected in any of the inboxes, instead of just a blank block of space. I don't know if there is any extension that does this (I could not find anything). I can replicate the image on start by changing the default URL in the settings, but it is gone after selecting a message.

(Edit for grammar)

[Jon]

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