I guess it could be if he didn't overclock. But at that point the 9900 with stock HSF would technically be enough. I'm not sure how these CPUs behave stock so hopefully someone with direct experience can chime in, but I would imagine that a beefier cooler would be better. Puget used a U12S from Noctua in their testing. It has a similar form factor to the Hyper 212 but outperforms it due to having more heat pipes. I believe it is also available in a black fan / black HS if appearance is a concern.
The Maximus XI Hero should be a great board. How much memory are you looking for, and why low profile? It looks like Puget uses 64GB in their "premier pro" systems, but they also mention that their premier benchmark uses less than 32GB, so I'm not clear how much is really necessary for this rig:
https://www.pugetsystems.com/recommended/Recommended-Systems-for-Adobe-Premiere-Pro-CC-143/Buy_192. This platform is not super picky about ram, so I would get whatever fits the budget and looks good to you or your friend. I would suggest getting two sticks vs a different number of sticks.
Your friend is going to want a fast NVMe drive to work with the large video files. Any Samsung 970 should fit the bill. Technically the Pro is the fastest, followed by EVO plus, followed by EVO, but they vary quite a bit in price and all of them are good, so get what the budget allows.
For the PSU please make sure you choose a well made model. 850W is more than enough for an overclocking system, though you could probably get away with less. Once you have a final component list, you can plug it in here
https://outervision.com/power-supply-calculator. I would greatly prefer a high quality 650W unit over a budget quality 850W unit for a similar price. The Seasonic Prime and Focus+ models, Corsair HX, and EVGA G2 and G3 models all come very highly regarded (it is not sufficient to look at brand alone, as Corsair and EVGA both rebrand units from multiple suppliers and have a wide range of quality depending on model). Edit: Re: 80+ rating - Gold is sufficient, and in the majority of markets (in terms of electricity cost) it will be very difficult to pay for the difference in getting a Titanium or Platinum model with energy savings.
Have you thought about an enclosure or case yet? They very widely in how they perform in terms of airflow and cooling, which will directly impact the amount of noise generated by the CPU and GPU coolers under load. Generally "silent" cases are more restrictive and they can dampen some noises that are unpleasant, but the fans usually have to spin faster to make up for it, negating most of the benefit. Check here for more case reviews than you can shake a stick at:
https://www.gamersnexus.net/guides/...ormalized-thermals-silent-base-601#!/ccomment