In Africa maybe, but not here in Europe.
Not so ! I am of an age where I go back a few years ! As a glider pilot I was frequently allowed entry in the cockpit and it was not uncommon I was offered the co- or captain's seat when either one needed a leak or a stretch.
Some of these crews were also glider pilots and familiar with my club and one, or two received their initial flight training in my club, where I was also one of the instructors. I remember KLM and BOAC in addition to Air Canada and Air Transat but not Air France.
In stabilised conditions, such as mid Atlantic, there is little reason for both pilots to be in their seats and the one pilot (flying) kept a weathered eye on important feedback from the instrument panel and radio x'missions.
It stopped when terrorists began airborne attacks. I am just one of the people who lost a privilege under the greater safety concerns for aircraft in flight. (and made the flight all the more boring what with a lower standard of service in standard class)