Kunming
There are two museums, Yunnan Provincial Museum and
Kunming
City Museum.
I have been to the Yunnan Provincial Museum and browsed, but there seems to be no storage space for large luggage. Anyway, I have never seen it.
Kunming
I have never been to the city museum, and in my estimation there is no place to store large luggage.

I hope my answer can be helpful to you.

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