A quick search on the NH-U9S shows it's a compact cooler for small systems, rated for up to 140 W (see e.g. [1]).
The 9950X's TDP (Thermal Design Power) is 170 W, its default socket power is 200 W [2], and with PBO (Precision Boost Overdrive) enabled it's been reported to hit 235 W [3].
> Noctua does not use TDP for their heatsinks and instead have CPU compatibility charts.
Reviewers and sellers do, though. Here are a few more: [1][2][3][4]
The highest rating is from [1], which says
You cannot access the TDP guide from here, but we will tell you that it displays 140W TDP; however, it also says you can overclock that to closer to 160W or 180W TDP overall.
AVADirect advertises it as good for 115W [4].
It also beggars belief that a single 92mm fan would suffice to cool a 9950X, when the best 120 and 140 mm air coolers just barely reach 240W [5]. The only Noctua in that review, the 140mm NH-D15S, gets to 233W.
> They say it's fine, with "medium turbo/overclocking headroom"
That’s a good catch, but don’t modern CPUs thermally throttle, rather than risk damage? Not that you should rely on this with an underpowered cooling solution but I would expect worse performance, not a fried chip.
There thermal paste on the whole CPU in TFA, it's just thinner on one side because there was more pressure there. Or are you looking at the pic of the heat sink, which is larger than the CPU heat spreader and thus only partially covered by paste?