Minecart 1.12.2
Forge v14.23.5.2838
Idō v1.0.4

I tried swimming in an area with only one-block deep water, but swimming doesn't work until I enter a spot with water at least 2 blocks deep.

Is your head under the water?

Yes. You must be under the water to start swimming. This is exactly the same as how 1.13 and 1.14 swimming works. Since this is not an issue I'm going to close the ticket

Alright, thanks