I have been using Canalplan for years and have found it incredibly powerful and flexible. But I just noticed that one of my most-used features now appears to be missing: the ability to mark certain places along the route as overnight stopping places, i.e. to override the computed stopping places. Has that capability been removed or might I have inadvertently altered some setting that is responsible for the issue?
No it's still there
The burger bar menu to the left of a place you add into the route plan allows you to mark it as a place to stop.