Please tell me, what should the ECU data flow and EGR be like?

Your tool is pretending to show you data that a gen 3 Prius does not supply. Where your tool thinks it is getting those numbers would be interesting to learn. It may have mistaken a Prius for some other kind of car.

 

You have said two things (that there are standard data, and that P0 codes are standardized) that are both correct, but not on point. The data you were showing in your photo in post 1 do not appear to correspond to any of the EGR data that a Prius will report. It seems likely the scan tool has a problem.

Here are the two live-data values the gen 3 Prius does in fact report pertaining to EGR:



Also, the reading from the MAP sensor (a reasonably standard PID) can be of use when diagnosing EGR.

Its usefulness is greatest when you have a scan tool that can issue active test commands, so that you can view the MAP reading response as you command changes to the EGR position. Without the ability to command changes, interpretation is difficult.

The most useful information you can get from the car about EGR is the result of the Mode 6 EGR test, where the car performs its own valve position changes, observes the MAP reading response, and summarizes the results for you as a test outcome.