The OBD port can easily spit out a read only mileage reading which is not tampering with the recorded value in the ECU. The OBD port is supposed to be user accessible and usable by the end user and 3rd parties (at least in the EU) even though manufacturers are trying their hardest to put “non diagnostic data” behind their proprietary software and/or wireless comms. Reading the data from the OBD port isn’t (at least shouldn’t) be classed as tampering.

One of the ways tampering happens on digital dashes that read the mileage from the ECU is by putting a interceptor in between the dash and the ECU as it’s easier than reprogramming the ECU. https://youtu.be/f4af1OBU5nQ

This comment was not clear. Odometer in car computer can be changed too. There exists special obd command to do this (when you need to replant ECU between engines), but you need to have a password (which is provided with "official" diagnostic computers/tools). If car has no mechanical odometer (most new passenger cars today don't), this is the only way to change odometer values.