Over the past couple of months, I have noticed that the coolant temperature on the highway doesn't reach 82C anymore like it did in the past. It stays around 79C to 80C max.
On high load like driving uphill or in stop and go traffic, the temps still go above 82C until the fan kicks in as it always has been in the past.
But on low load or driving on the highway, it doesn't go over 80C anymore.

I had prophylactically replaced the thermostat in 2019 (about 80'000 km ago) with an AC Delco 131-158. Could it be the thermostat? Or something else?

 

Try burping the coolant system, perhaps replace the coolant if you haven’t since 2019

 

82C is not too low 80C is. when idling does it go above 82C?
I suspect he t-stat.

 

Thank you for your replies.
I replaced the coolant last year. Yes, may try to burp it again.
When idling, it does go above 82C, up to 87C -> I didn't wait any longer.

 

The fan should turn on at about 104C.
If you can get a laser thermometer you could test the temp sensor by pointing at the t-stat housing.