Don't even try it.

No. You cannot mix DDR4 and DDR5 in the same system—even if the motherboard has slots labeled for both. That board doesn’t exist for consumer hardware. Motherboards are built for one memory standard, period. If you force sticks into the wrong slots, nothing works. The system won’t post.

Performance doesn’t come into play because it’s physically incompatible. Different notches, different voltages, different controllers. Save yourself the headache and buy matched sticks of whatever your board actually supports.

If you see a motherboard claiming to support both, it’s a typo or you misread the specs.