Some fridges can be quite marginal...
- Some require the bottom "vegetable & debris bucket" to be in place
and a shelf set correctly
- Others do not like working unless there is something in there to
cool

The only way to really know fridge temperature is a glass of water &
thermometer.
It should really be no more than 7oC and the ideal is around 5oC
(although certain foods have more specific requirements like cheese,
lettuce, and so on).

Critical maintenance is preventing the rear fridge cool plate from
icing up - on some slimline Inde**** this basically makes the fridge
temperature climb inexorably away from safe levels. Common failure
modes of fridge freezer is for the thermostat to fail - in some cases
jamming on (usually noticed by £120+ increase in electricity bill and
paint burnt off a very rust-orange compressor).

Measuring air or object surface temperature is pretty pointless.
This not withstanding a professor moron of john moores was observed
jumping around on BBC television news after "discovering" that surface
temperature of objects rose markedly when the door was opened. Within
even 1 millimetre of the objects surface the temperature was of course
quite normal. I guess he also believed insulation was perfect too.
Quite how he got an O-Level in physics never mind a professorship is
beyond me.

I might be the odd one out, but I think all fridge/freezer
manufacturers *should* be forced to provide LED temperature displays
for both. I suspect they have not purely because many products are
actually quite marginal with either minor ice build up (and never mind
the fun of frost free). Alarms could be an lucrative optional plug-in
extra like a card, SMT piezo & bit of logic - like a big SD. Can not
understand Bosch putting the green/red lights behind the door seal so
you can't see them without opening the door. Genius. They do have a
dial thermostat in the door which has ambiguous markings.