I don't think that they are checking all passports, especially during busy periods but it only takes a diligent border officer on a quiet day and you're nicked. I think it's that fear that will keep most non residents abiding by the rules.

I wouldn't mind having passport stamps. I have permanent residence card issued by Germany and based on the trips i have done in the past 3 years, i can summarise my experience as follows:

Germany, Austria, Switzerland and Nordics: if i show my German residece card together with my UK passport, no stamp
Italy, Spain, Portugal: Always stamp (I asked Venice Airport why they stamped my passport, they said because it was issued by another country, they couldnt check if it was a fake one or not...speechless)
Eurostar France: if i show my German residece card together with my UK passport, no stamp
Marseille, Nice: Stamped...

Unfortunately i have never had experience of entering EU from other EU countries...

I wouldnt mind seeing my passport stamped...but what annoys me is that sometimes, when i enter, no stamp, when i leave, stamp...quite difficult to see all EU countries act on the same page...:-(

"Unfortunately i have never had experience of entering EU from other EU countries..."
You mean just travelling from one EU country to another? Where there are no passport checks anyway?

Mostly, but if the EU country you are entering isn't in Schengen like Ireland, there is passport control.

I was generalising.

There's also the scenario where a Schengen country has temporarily re-introduced border controls, which is supposed to happen only in exceptional and justifiable circumstances and for a maximum period of 6 months. In practice, some countries have extended this provision well beyond the 6 months limit.

France currently seems to be operating some internal schengen border controls - I flew in to Paris from Portugal a week ago, where there was no passport inspection on arrival, and back to Portugal from Carcassonne, where there was. No stamping, but definitely a passport control check on exit.

Shall we make a list of when you will have to show your passport?
Or ID card? Or should they be separate lists?
Or should we accept that generally you don't?
On a personal level I cross EU borders frequently and it was probably in covid times when I had to last show ID of some sort.