It's called Distributed Propulsion, and it theoretically has advantages over normal aircraft propulsion. Presumably using dozens of piston or turbine engines has enough drawbacks to make it not worth it, which is why it hasn't been a thing until electric planes became possible.
With a conventional turbofan (or basically gas-anything) the bigger it is the more efficiency gains can be realised. So I'd expect that conventional jets would really ideally have just one engine, and they typically have 2 or 4 for reasons of fault tolerance and isolating noise from the fuselage.
None of this applies with electric, particularly a cleansheet design.
But then they would've been using many smaller ICE or jet engines already to get redundancy. I suspect the reason is that it's easier to get that kind of redundancy with electric motors - they're more compact, lighter weight, less overhead for each.
We do. It wasn't until the 80s that twin engine airliners were certified for long flights. Before then it was 3 or 4 engine only. It took a lot of effort to get jet engines that reliable too.
Single vs dual engine helicopter is a big safety distinction. There's heavy lift and military helicopters with 3 engines.
