They can be mixed off traffic is rather low and the path is wide enough (basically plan for the encounter of a pram in one direction with a cyclist with trailer in the other direction). But that typically doesn't work for sidewalks in many cases because they're either too narrow or have too much foot or bike traffic.

E-bikes and cargo bikes are also a lot heavier than other bicycles and are getting more common. Due to higher mass and being powered they're quite a bit more dangerous to pedestrians.

This generally works were the traffic is low, in sub urbs and on specific paths(not sidewalks in metropolitan areas). combined pedestrian walk and bicycle paths are possible, in sub urbs and in more rural areas, though even there they should generally be split and only used for overtaking:

https://www.osteraker.se/images/18.5bb0400617c11d33b551007/1...

In bigger cities where the foot traffic is high, it's absolutely not possible, in my opinion.