Are large jet turbofans so easy to spin?
Yes, large turbofans can be turned by hand without too much force. On smaller aircraft this is regularly done as part of the preflight walkaround. You can see an example in this YouTube video of an A320 walkaround:

Admittedly, the pilot turns the engine with four fingers here, but you can see that not much force is required. Turning it with a single finger would easily be possible.
On a larger aircraft like a Boeing 777 you cannot reach the fan when standing on the ground in front of the engine. Spinning the fan by hand is therefore not usually done during the preflight.
This video shows a GE engineer turning the fan blades of a GE90 (the predecessor of the GE9X) engine by hand:

Again, it is not one finger, but he is not using much force to turn it, so it should be possible with one finger.