If you're in survival and place a boat in water, and then jump onto it, and then jump multiple times straight up in the same position and then jump on land, you will receive major fall damage.
Check out this YouTube video of me reproducing the bug: Minecraft Boat Bug - Version: 19w42a
Thank you for your report!
We're actually already tracking this issue in MC-153698, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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