The Apollo service module provided power etc. to the command module through umbilical connections covered by a fairing. When the two modules were separated, a 'guillotine' cut through the cables and the fairing opened. It can be seen at the top of this Apollo 13 image from Wikipedia:
The Dragon 1 and 2 (uncrewed and crewed respectively) have a similar device called the 'claw', between the trunk and the crew module (visible in the centre of this Wikipedia image):
During the recent re-entry of demo flight 2, the claw was mentioned as part of the trunk separation procedure.
I believe the purpose of these devices is to avoid routing cables through the heatshield. I've never noticed a similar connection between the corresponding Soyuz modules, is there such a thing or are services supplied in another way?