How to reproduce: build a structure like the one on the screenshot in the air and leave the hole at the end of rail track (right part of the structure). In the same Y coordinate as that hole put water at the ground level and surround it with blocks. Then go in survival, put a minecart on the rails and sit in it. Go in the direction of the hole until you stop moving. Then break the last rail and the block below it, that way the minecart will be between two blocks falling down with the player in it, it should land in the water and on the solid block. It result in that death message.
Thechtoto
Still works in 1.16.2
How to reproduce: build a structure like the one on the screenshot in the air and leave the hole at the end of rail track (right part of the structure). In the same Y coordinate as that hole put water at the ground level and surround it with blocks. Then go in survival, put a minecart on the rails and sit in it. Go in the direction of the hole until you stop moving. Then break the last rail and the block below it, that way the minecart will be between two blocks falling down with the player in it, it should land in the water and on the solid block. It result in that death message.