This is not generally required when travelling between Schengen countries. National governments may introduce immigration checks within Schengen, and in recent years have sometimes done so for particular reasons e.g. during Covid lockdowns or due to a sharp increase in refugees/asylum seekers. But these are short-lived and it is not the norm.
It isn't clear if you meant this as an aside, but Switzerland is a Schengen area country. It isn't in the EU/EEA which (in some sense) necessitates customs checks more so than immigration checks, but nonetheless there are frequent checks on the border with its neighbouring countries which are in the EU/EEA. It's less common by private vehicle, in my experience.
It seems that nothing is so permanent as a temporary Schengen border control. Some of them have been in place since 2015 and it doesn't look like they'll go away any time soon. In fact Germany is looking to expand them, adding border controls on its Czech and Polish border.
> This is not generally required when travelling between Schengen countries.
It happens more and more due to illegal immigration. I've beens topped in trains, buses, highway parking, by police officers asking of passport and reasons to travel.
In Paris/Marseille/Strasbourg I've always been controlled since ~2020
