It used to be that boats could be steered by pressing A or D or by using the mouse. Now keyboard steering is gone, with no improvement whatsoever to mouse steering. Maybe this is not a bug and you did it on purpose, in which case there must be a bug IN YOUR BRAIN.

With boats in Minecraft, keyboard steering is vastly superior to mouse steering. Before, I could instantly start turning hard to the left or right, and continue looking where I'm going while steering. And my maximum turning speed was much faster. And I could use the S key as a brake. Now turning is sluggish to start, slow at maximum turning speed, and I have no brakes. Rivers are totally unnavigable now, and whenever I use a boat I have to plan on crashing at my destination. (Well, I guess I could ride a boat down a river without crashing if I go way, way slower than walking speed, which of course totally defeats the purpose of riding a boat on the river in the first place.)

Generally speaking, players don't like it when you take away options for no god damn reason. There is no reason for this change. You can't say you did it for realism, because in real life you can, in fact, turn a rowboat quickly, turn it without even moving, and you can row in reverse to stop quickly.

This is particularly horrible in my current world where I used to always use a river to get between my new base near a witch hut and my old house and mine near my spawn point. Now that I can't use it, I have to walk through desert 1/3 of the way, walk on swampland 1/3 of the way, and swim through swamp water 1/3 of the way.

In summary, the crippled boat controls make rivers useless, and on the occasion that I use a boat to cross a large body of water, I usually crash-land it. I TRY to save the boat by turning 180 degrees and then pressing W before hitting land, but I usually fail.