You can use 4 sticks - many people do, it's just harder to get 4 sticks fully stable, especially at higher speeds, so using 2 is recommended by many people...plus the speeds that can be achieved with 4 sticks is often lower. Just be careful if buying 4 and check the experience of others etc.
Z690 Hero, BIOS 2305, ME Firmware 16.1.27.2176, 7000X Case, RM1000x PSU, i9 12900K, ASUS TUF OC 3090TI, 2 x 16GB Corsair RAM @ 5200MHz, Windows 11 Pro 22H2, Corsair H150i Elite AIO, 4x Corsair RGB fans, 3x M.2 NVME drives, 2x SATA SSDs, 2x SATA HDs.