In my first 1.18.0 world, after travelling distances, with a map in hand, boats disappear when you exit them. this has happened with Spruce, Dark Oak, and Birch. I retraced my steps and couldn't find it, which makes me think it isn't just an issue with the boat location updating incorrectly. Also, parrots can no longer sit in boats. I do a lot of water travel and exploration, I noticed it within a few minutes of creating the world.