When I downloaded the Creeping Winter DLC, on the Map (mission select screen) when selecting a level, It won't let us change the difficulty when playing with a single Joycon as a controller.

I believe the issue is that both changing a mission, and difficulty are mapped to the same button, so when pressing SR or SL to change difficulty it will instead change the mission.

See video attachment.

Minecraft Dungeons  Build 1.4.2.0_311

I put 1.4.3.0 above because there was no option for 1.4.2.0_311