"Another example: ask a young person who has only driven cars with catalysts fitted, and he / she won't be aware of the possibility to start a car (if it has no catalyst) by pushing it to a downslope. "
I remember years ago a woman asking my pal and me if we could give her a push start. We started pushing the car, next thing we hear is this clicking noise and the starter motor trying to turn........... Anyway gave her a quick lesson about bump starting and she was soon on her way.
Talking of bump starts I've learned to check that the driver really knows how to do it before offering to push. So many folks pick first gear and lift the clutch right up, it's not fun head butting the rear of cars.
As for cars with cats, if you are sure it's just your battery that's a little weak or a bad contact on the starter, it's probably OK to bump start it. Cats do not like neat or unburnt petrol/deisel, that's what does the damage and why they say don't dump start em. Also even if it's just the battery, maybe proceed with caution, sometimes strange things start to happen to the digital systems fitted to modern cars when the battery voltage drops and it might not catch.
At least cats are much much cheaper than they used to be ten years. Though why we bother with em beats me, they are pretty much useless devices.