How feasible would it be to bombard the enclave with radiation, low enough to avoid any physical damage to the silicon, but high enough to cause random glitches in computation.
To flip bits, you'd generally want to use radiation with a high local energy deposition such as alpha particles or heavy ions. With typical photon radiation (X-Rays or gammas from radioactive decay) you'll mostly just degrade the silicon until it stops working reliably overall, and not change data.
As the secure enclave's surface is much smaller than the application processor's you'd also have to focus your protons/alphas/heavy ions very well, because otherwise you'd affect the logic outside of the secure element much more often.
I think this approach in practice is much, much harder than to just shine any random radioactive source on it.