Welcome to the forum!
When you look inside the fridge, under the freezer, on the cooling fins there should be a Thermistor plastic device clipped on to one of the fins. This should be on the right fin, and should be slid up to the top of its range. There may be a label on the right inside of the fridge to confirm this.
Not sure if you pre-chilled you fridge before your trip, but that is a must. Also do not add warm grocery items into the fridge, it is not really designed to handle that. A separate cooler in the tow vehicle works to pre-chill things.
You can buy some ice to put in the fridge temporarily to cool it.
What is the air temp where you are, and are you in direct sunlight? If your exhaust fan is not working right, that would compromise things. [edit -- sorry just saw your sun location -- yes fan should be going on, and it should be noticeably loud if it is OEM. Did a prior owner put in quieter fans maybe?]
Also there may be an inline 12-volt fuse in its own holder near the fan (ours is behind our switch by the entry door). If the glass fuse is blown, that is a simple fix. Ours is only 1 amp 12v
DC as I recall, but yours may be different.
Here are some older threads when you have time to read them:
Also if you go "up" to this sub-forum's list of threads, you can peruse the many pages for relevant posts:
PS -- Yes your photo shows a suspect switch IMO. Do you have a voltage tester meter with you? They are cheap in auto parts stores, and will help in the diagnosis of many 12-volt problems.
And yes, you should hear the fans kick in especially if you are outside looking in.
Not sure how detailed your owners manual is, but it worth a peek there too, especially if they show the Thermistor adjusting in a photo or illustration.
Sorry for the long PS, but is everything else in the trailer working? Lights, water heater, gas cook top burners etc.? What is your battery voltage readout on the monitoring panel?