Older fridge cooling Better on 110 than propane

I would check the burner for debris.

Light scale can fall down the flue and settle into the burner, blocking the flame somewhat, thus reducing its efficiency.

I've had that happen a number of times.
Pull the little wind guard flap off, get in there initially with a small vacuum with a tiny nozzle attachment to get the visible stuff, then compressed air to blow it all clear.

Careful not to blow stuff back into the propane outlet line.