Different airports do this in different ways.

As long as any rules on separating “clean” passengers from “non clean” passengers or for flights where people must clear immigration then all is good.

For example an ex UK arrival into AMS I disembark into the gate area (meaning I can do a back to back TP run or connect directly to another non Schengen flight) but flights from other countries get directed through a separate process of re clearing security even if they aren’t entering the Netherlands.

quite possible. There is no guarantee at uk domestic that you will disembark directly into the departure area.

Depends on the set up of the airport.