What will happen if I mix DDR4 RAM and DDR5 RAM in my PC?

ddr4 and ddr5 same slot   Dan ddr4 sodimm slot

Physically, a DDR4 module, looks very similar to a DDR3 Refer to your motherboard documentation to make sure that it has the correct DDR4 slot

DDR5 has lower latency than DDR4, thanks to its improved architecture and design For example, DDR5 has a new command called SAME-BANK DDR5 RAM has a higher base speed, supports higher-capacity DIMM modules , and consumes less power for the same performance specs as DDR4

iron bank free slot Like the previous generation transition between DDR3 and DDR4, each manufacturer's Z690 series all also have versions that support DDR5 and DDR4 So most likely there won't be any AM5 Motherboards with both DDR4 & DDR5 DIMM Slots on it since DDR4 and DDR5 are not compatible to each other