Piglins sit elevated in boats and minecarts.
They can get out of them by themselves. In boats, they can stay on the head of the player when he leaves the boat. The latter two issues appear to be related to the fact that they don't sit inside the boat to begin with.
Linked issues
Comments 2
Duplicate of MC-184619
Thank you for your report!
However, this issue is a Duplicate of MC-184619.
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