When 3.3 volt is given to the analog pins, they give a value around 800 (AnalogRead). Expected value of 1024.
Analogwrite on the analogpins with value 255 gives 3.3V. So this this is a little confusing.
Is the analogPins (on the MKR GSM 1400) 5V inn and 3.3V out?
Ps: analogReadResolution(10); and analogReadResolution(12); Giving the "same" result.
No, don't apply 5V to any of the pins as this is above the absolute maximum voltage ratings.
You should get a value of 1024 with an input of 3.3V. Can you connect your analogue pin to VCC with nothing else connected and try again? If you have anything else connected to that pin it could be affecting the voltage.
I have run in-depth tests of the A/D converter in the MKR-GSM-1400 unit I have, and it handles 5V just fine.
With 5V from a certified power source, all analog pins give a value of 1024.
PS: Don't try this, unless you're 100% sure what you're doing. There may be multiple versions of the GSM-1400.