Mostly the former. There’s nothing expensive about decapping a chip and tossing it under an electron microscope.

A it’s not just an electron microscope but a cryo probing stations for sub 22nm lithography are insanely expensive.

You can’t simply decap and image a multi layer chip it’s not 80’s era masked rom.

How much time and effort would it take to go from a chip under an electron microscope to the embedded crypto key, though? Seems like a substantial reverse engineering effort. (Although only for the first time you do a particular type of chip.)

An electron microscope alone won’t work not to mention you have a high likelihood of damaging to chip as the voltage of the electrons deposited on the sample can exceed what the IC can tolerate.

You need a cryo probing station of some sort I’m not sure if these even exist for 12/10/7nm logic yet.