Main differences between x670 and z690 motherboards:
x670 motherboard is amd platform, am5 interface, only support ddr5 memory, can support amd Ryzen 7000 series CPU, the best collocation is 7700x, 7900x, 7950x and so on.
z690 motherboard is Intel platform, LGA1700 interface, support ddr4 and ddr5 memory, can support Intel 12 generation CPU, the best collocation is 12700k, 12900k and so on.