Fritz from Austria foils just above a cold (I'm assuming) and still lake
Fritz: "It was a phenomenon I have not seen yet; the wind just did not touch the water but was blowing only a bit above the surface...yes, it was a mind blowing experience as I could not believe I am flying and I could not see where the wind is coming from"
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Is it an efoil? The sailor seems to be hiked out against the sail so maybe not.
A French windsurfer posted something similar but with a Formula board
https://www.windsurfing33.com/forum/viewtopic.php?f=42&t=121360&p=868839#p868839