Research about a case that works for you. Some like a Lian Li case, some like a Fractal Design case, a few like a be quiet! or Corsair case, or NZXT case, look at different options. Then, an x870-E motherboard, maybe a Gigabyte Master or ASRock Taichi, Ryzen 9950x processor, 64GB RAM, and a RTX 5090.
Due to overheating issues, I would not buy the best everything. Something like x870-E AORUS MASTER with 9950x, no x3D, and only an MSI RTX 5080 SUPRIM SOC, not 5090, 64GB RAM, USB DAC, and 1000w or 1200w. 1440p with DP 2.1 480Hz.