Leeberator

I'd start with adding another NVMe drive - ideally 2TB. If you get a Gen 4 one, you can move the SN550 to the second slot. Then you can have one OS drive and another drive used as a scatch disk, which should boost scrubbing performance in Premier.
 
If you don't like the performance of the stock cooler, I'd actually go with a dual tower cooler, like the DeepCool AK620 or Scythe Fuma 2. It'll be cheaper, and you won't have to worry about pump noise.
 
And since you use Premier, I'd upgrade to 32GB of RAM, or maybe even go to 48GB by adding a 32GB kit.
 
Those 3 upgrades combined should be under $400, and should make your editing life much better.

You really can't go wrong with either, but if the 3600 kit is really only $25 more, you might as well get it. The only reason I'd save the $25 is if that was make or break for the budget of a more important component.

+1 for the Galaxy A50. I sell them at work, and they're great. Pixel 3a competitor for less money, with both a larger screen and battery.

Drive 0 Partition 4: Crow - 236,6GB
Drive 0 Unallocated Space - 693,0GB
 
236,6+693= 929,6GB

It could have to do with the slots the cards are in. Some boards have x16 slots that only operate at x8 speeds depending on what's plugged in where. Your 40-lane CPU makes this less of a possibility, but it's definitely still on the table.
 
Check your motherboard manual for a list of PCIe modes.

this is why the windows installer tells you to make sure you're installing the right version for the key you have.