DDR4 and DDR5 cannot be mixed.

No, you can’t.

They’re physically keyed differently — the notch in the connector is in a different spot. Even if you could force a DDR5 stick into a DDR4 slot (you can’t without breaking something), the motherboard’s memory controller is built for one standard or the other. Not both. Some newer boards support both, but they have separate sets of slots for each type, and you can’t use them simultaneously.

So if you have a DDR4 motherboard, DDR5 won’t fit. If you have a DDR5 board, DDR4 won’t fit. No dual-channel magic will save you.

Don’t try to force it. You’ll just waste money and possibly damage the slot.