Hi. This error pops up when making the circuit in the designer. Does it work for you, when you choose ATmega328P as the controller and then add an NRF24L01 component?
I get the same error. A notification appears at the bottom of the screen with a link to “Details” which opens a dialog with the title “Can’t read solver’s error” and a link to “SHOW OUTPUT” which then shows the JSON you pasted:
I’d suggest you make two circuits, one for your ATmega328P and the other with an Arduino so that you can get the code. You’ll need to modify the wiring to match the ATmega328P pins of course.