Hmmm... I have NRST unconnected too. Didn't put a cap on it because the debugger drives it. But presumably 10nF should be safe?
Given it has a ~40k pullup, one would need a fairly powerful radiated spike to pull it down for long enough. This is the data sheet, showing 100nF
The very point of my post was, the reference manual, where this information does not belong at all, gives completely different rationale for the capacitor: it is Just Needed. They don't give the exact reason, but at least H743 with external Vcore* fails to start without the capacitor, and it has nothing to do with EMI or radiated anything, the test environment was quiet and I probed that pin to verify clean signal - rising fast, though, as expected without the cap. The CPU clearly needs the slow ramp on the pin, lengthening the internally generated power-on reset pulse.
*) I'm mentioning this because it could be important, even though the thing should boot with internal LDO regardless, but maybe there is some weird power sequencing thing going on. In any case, the capacitor is needed per the reference manual, and not needed per the datasheet. That's the point. You have to read all the documentation carefully.
It's actually quite classical to somehow f*** up the internal reset circuitry. Early AVR devices were known to have issues to the point people designing in external power-on-reset driver ICs. Later AVRs supposedly fixed it, but still
required smaller external pull-up and some official programmers denied working if they did not detect the correct amount of resistance.