No final de Avengers: Infinity War, Tony Stark and Nebula are stuck on Titan.
But they have the Benatar which can use the jump points as we see in Guardiões da Galáxia Vol. 2 when Rocket made 700 jumps.
So why didn't Nebula think about making a few jumps to get back to Earth? Had they ran out of energy? Is it to complicated to calculate the way home even with one Iron Man on board? Or did I miss the point, and this ship just can't jump at all?
There's no indication that they weren't trying to use the jump points, in fact they were most likely trying to use them. However, you need to be able to get to a jump point to be able to use it, they aren't summoned. We see this in Guardiões da Galáxia Vol. 2 when the Guardians are escaping the Sovereign fleet.
Peter Quill: What’s the nearest habitable planet?
Gamora: It’s called Berhert.
Peter Quill: How many jumps?
Gamora: Only one. But the access point is 47 clicks away. And you have to go through that quantum asteroid field.
Guardians of the Galaxy Vol. 2
Even then when using the jump points the ship still needs to use fuel as it needs to travel between jump points if there are more than one. And as they are on Titan it seems most likely that they needed to use more than one jump point. We see this when Rocket plots the course to Ego in Guardiões da Galáxia Vol. 2 as mentioned in the question.
As we see at the start of Vingadores: Fim do jogo the Benatar had been damaged in the fight with Thanos, specifically the fuel cells, and they only managed to give the ship a small amount of life. Apparently it wasn't enough to be able to get them through all the jump points they needed to use to get to Earth from Titan.
Tony Stark: Some fuel cells were cracked during battle, but we figured out a way to reverse the ion charge to buy ourselves about 48 hours of time. But it's now dead in the water. We're 1000 light years from the nearest 7 -11. Oxygen will run out tomorrow. And that'll be it.
Avengers: Endgame