Simulate radiated immunity in Spice
In LTSpice and the like you can't calculate/estimate conducted emissions nor radiated emissions of your PCB/product.

For radiated emissions you need a 3D electromagnetic simulation software.
That kind of software calculates E(x,y,z,ω) and H(x,y,z,ω) inside and on the surface of a user defined box that encloses your PCB.
Afterwards, through the Equivalence theorem it calculates E(x,y,z,f) and H(x,y,z,f) at any point in space outside the box.
f is treated as a parameter where the user specifies it's interval.
For example:  30 MHz &lt; f &lt; 1 GHz

More info here:
https://en.wikipedia.org/wiki/Surface_equivalence_principle

To model immunity of your circuit to external incoming RF fields, you have to model the external field E and H excitation using distributed voltage and current sources.
See here:
https://www.researchgate.net/profile/Changyul-Cheon/publication/263403050/figure/fig1/AS:296053577404419@1447596081508/Modeling-of-external-field-excitation-of-a-TL-using-distributed-voltage-and-current.png
LTSpice is not able to do it.
You need a 3D electromagnetic simulation software.
You will need to import your PCB as a 3D model file.
You will need to know and import the IBIS model of all I/O pins you need to monitor.
You will need to introduce in the 3D scene a radiating antenna that act as a source of radiation.