The first 20 minutes is about the normal content creator, who uses normal DSLRs or MLUs, shoot at 4k or max 6k, does not do a lot of noise reduction, fairlight, color grading etc. Just the normal editing stuff.
Most important is to get the studio version of DVR (around 300€/USD). Without it, you can not benefit from the speed optimization.
For this kind of user, the PC does NOT need to have the best/fastest graphic card with most RAM. 8GB RAM on that graphic card is enough, because DVR does not use the GP that much in this use case. NVidia is recommended for graphic cards.
What is far more important in this scenario is an Intel i core (i7 or i9) with integrated graphic card, because you need this for the decoding of the normal cameras. Intel has a special feature in these chips for this. Makes it way faster than the encoding over the graphic card. Make sure that the iCore graphic chip is enabled in your BIOS. Some PC disable it, when they detect an external graphic card
Use a fast M.2 SSD for the operating system. Samsung recommended. At keast 1TB to get the versions with reading/writing speed of 7GB. For storage, normal SSD are fine (non M.2 versions).
Get RAM for your PC. 64 GB RAM is enough for 4k/6k and this use case.
Buy quality parts. Nothing cheap from. AliExpress. Do not save on the wrong end. Here is the overview at around minute 20 in this video.
Next use case is the more demanding filmmaker. If you use a dedicated camera for filming like a RED and do more with fairlight, color grading, noise reduction, 8k videos etc., you only need to bump up the gear a little bit from the previous use case.
64GB-128GB RAM on the PC, more SSD storage and a better/faster graphic card with more RAM like a 4080. Explained in the video from minute 20-25.
Third use case: If you do the really crazy stuff in filmmaking, then you have to go crazy with the gear too. But do not make mistakes, which will at the end slow down your system. Explained after minute 25 in the video.
For Fusion you need a different focus. Since BlackMagic bought Fusion 8 years ago and just put it into DVR, it needs a different hardware to speed up. Talks about this from minute 26 on.
Single Core speed and PC RAM are the most important factors for Fusion. A fast graphic card does not help you with Fusion.