My mini-ITX build has been great.
Gigabyte A520I AC AMD AM4 Mini-ITX Motherboard
Zotac NVIDIA GeForce RTX 3060 Twin Edge Overclocked Dual-Fan 12GB GDDR6
Corsair CX650M 650 Watt 80 Plus Bronze ATX Semi-Modular Power Supply
AMD Ryzen 5 3600 Matisse 3.6GHz 6-Core AM4 Boxed Processor - Wraith Stealth...
Corsair VENGEANCE LPX 16GB (2 x 8GB) DDR4-3600 PC4-28800 CL18 Dual Channel ...
Crucial P5 Plus 1TB SSD 3D NAND M.2 NVMe PCIe 4.0 x4 Interface Internal Sol...
NZXT H210
About $800 all told.