Exactly the opposite of MC-164692. I do not know why that was "fixed", it was not a bug.
Entering a boat or minecart has nothing to do with a hand or an arm. I have entered multiple real-life boats in my life without needing to use my arms at all.
When you mount a horse, it now even looks like you're punching it.
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Hm, didn't notice that MC-164692 was only about boats in specific. I'm reopening this ticket, but expect it to be closed as WAI or Invalid.

Any action taken by the player that results in something happening should result in an arm swing, as this is an indication to not only the current player, but to other players, that something was done.
As you already noted, since MC-164692 has been marked as "Fixed", this behaviour is confirmed to be working as intended.
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