They need to track time in the Schengen zone for non-EU citizens, which is what the stamps are mostly for AIUI.
Common in/out the Schengen with my UK passport post Brexit - got lots of stamps. Though it varies by country
Every round trip from the USA to Ukraine gets six stamps for me. I’m going to have to renew about five years early on this passport. I’ll get the fat passport next time.
I’m a US citizen and get stamped on the way in and out of Schengen area every time. I think they do the same for UK post-Brexit.
My UK passport has been stamped on every EU entry I've made since Brexit, except Ireland.
I’m not sure what you’re referring to. Where are you traveling from? I never had my EU passport inked when traveling to the UK or US. Within the Schengen Area I never needed a passport.