The strange button is an easter egg located in the Museum Storeroom. The button looks like turquoise and orange stone. When examining it, a popup message appears which tells you that the button is broken beyond repair and something about the letters NMM.
The message refers to Nexus Mod Manager. Because Legacy of the Dragonborn is a large mod it requires manual downloading, and thus cannot be installed using a press of a button in a mod manager.
Location
The strange button is located in the Museum Storeroom on the table straight ahead of the entrance door, on the table next to the Classic Museum's model.
Contents
This appears to be a strange button of sorts and only the last three letters can be translated as NMM, but it is clearly broken beyond repair and without any hope of functioning properly... Best not to ask about it.
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