RV fridge not getting cold on propane, but freezer works?

I’d bet your LP pressure is low. If the fridge cools fine in AC mode but not LP, you need to have the LP pressure checked with a manometer. You can’t judge the pressure just from the flame appearance.

I’m assuming you DO have a flame when it’s running on propane, or you would have mentioned a check light or error code indicating a flame failure.

Your regulator should be adjusted to maintain the gas pressure at 11” of water column with one of the bigger LP loads running, like the water heater or the furnace.

:):)