There is a bug in DND with gboard. I'm not sure if this is a firmware fault, oversight or issue with gboard.
If the Gboards haptics are set to 'default' the keys still vibrate in DND. If I change it to a numeric value (8ms feels about the same as default btw for other S20 Ultra Users), there is no haptic feedback when DND is enabled. No haptics is what I would expect in DND.
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One UI Beta Team