On Minecraft Bedrock Edition, how do you find Mooshrooms?

In Bedrock Edition, Mooshrooms only spawn at a light level of 7 or higher, and in the Mushroom Fields or Mushrooms Field Shore biomes:

Mooshrooms spawn at light level 7 or above in Mushroom Fields and Mushroom Field Shore biomes. 5% of them spawn as babies.

What makes it hard to find them is that the particular biome they spawn in is quite rare. These biomes seem to generate most commonly as islands in the ocean, so perhaps start searching around any oceans.

The mushroom biome usually generates as a single island surrounded by ocean, though it occasionally generates touching land on a side