The MediaTek wifi AX platform is supported by OpenWrt master and also supported by upstream Linux including AX wifi. (MediaTek contributes a lot to upstream kernel)
* MT7622 SoC (2x Cortex-A53, including 4x4 ieee80211n wifi integrated in MT7622 and supported by upstream kernel too)
* MT7915 Wifi 6 (ieee80211ax) 4x4
* MT7530 5 port 1G switch (2.5G uplink)
You can find this hardware in the following devices:
* Linksys E8450 / Belkin RT3200 (same device just different name and color of casing)
* Ubiquiti UniFi 6 LR
* Also some others
Unfortunately the Linksys E8450 is unavailable in my country (Poland) or is ridiculously expensive. I settled on a Totolink X5000R which supposedly is supported by OpenWRT and has a Mediatek MT7621A. I will receive it in 2 days and test it.