In a video I published in 2022 (How do EMR pens work), a specific method to detect pressure is shown. This method involves moving the ferrite core which then alters the resonant frequency of the LC circuit. This design is from a very, very old EMR pen design.
Modern designs use a separate pressure sensor which is more reliable for detecting pressure.
The OLD EMR pen design can be seen in this teardown of the Huion PEN80 pen.
This pressure detection mechanism is discussed in great detail here: