Will a Wi-Fi 6 extender work with my older Wi-Fi 5 router?

Yes. Wi-Fi 6 (AX) extenders are backwards-compatible with Wi-Fi 5 (AC) and earlier routers. You won't see Wi-Fi 6 speeds on the backhaul to an older router, but the extender's own radios can still deliver Wi-Fi 6 to nearby Wi-Fi 6 client devices like newer phones and laptops. Reviewers across the data we read generally recommend buying Wi-Fi 6 even on older networks for the longer device support window.