Right disclaimers first, we've seen comparable stories with Comet Lake before release, which turned out much better in the end. None the less as the titles say, an all-core boost on the pending Rocket lake Core i9 11900KF resulted at 98 Degrees C under all-core load.

You can fire off many scenarios here, wrongly installed liquid cooler, power stage PL2 locked at 250 Watt for a far too long time, incompatible or unrefined BIOS applying wrong voltages ... and well fill it in yourself. 

Some folks at the Chinese tech forum ChipHell have access to Core i9-11900KF and when they stressed it at what seem to be stock settings (all-core boost frequency of 4.80 GHz) it would hit 98 Degrees C, and that's on an LCS cooler 360mm as configuration. AIDA64 was used in the FPU stress test to create load, normally on such a cooler and say Comet Lake, you'd hit 80 Degrees there. CPU-Z reports a core voltage of 1.401V which I find too high and thus that can be the reason behind the high temps. Make of it what you will, but if it's the voltage then tweaking Rocket lake is going to be difficult.

Additional sources: 9550pro (Twitter), ChipHell Forums

Core i9 11900KF Sample Hits 98 Degrees C cooled with 360mm AIO Under Load