Opinion please on a high end Unreal Engine/Editing build

I have 3 concerns:

1. If you plan on using the Dominator memory, you will have to manually set the D.O.C.P. profiles for AMD since the ram is not AMD EXPO certified.
2. The Corsair H170i will not fit in that case, you would have to go down to the Corsair H150i instead.
3. For the 2TB SSD, I would suggest something faster, such as the WD SN850X or the Samsung 990 Pro, which can generate read speeds up to 7,450MBps.

As far as the processor, the faster the processor can preform, the faster it can render objects in real-time.

The Ryzen X3D chips are still somewhat iffy in certain applications, even losing to their non-3D counterparts. Thankfully Unreal is one of those where the chips shine so I think they are a worthwhile investment. But for your editing needs, it would be best to either switch to an Intel system for Adobe Premiere or really any of their suite of programs. If you use DaVinci, while AMD is more analogous, the X3D chip actually loses to the non-3D chip in overall performance. As the adoption of support for X3D becomes more standardized you should see many of these anomalies disappear but at least keep them in mind if you find strange performance results.

I also highly highly recommend getting a large capacity external SSD for doing routine backups or investing in some form of RAID capable NAS. I have lost more than my fair share of data over the years due to over-writing SSDs during video editing and hate seeing similar things happen to others!

Everything else considered I think your build looks good!