I worked out how to set the Tx MCS  -> iw dev wlan0 set bitrates .....
But I'm trying to work out if it's possible to set the Rx MCS on the AP or if that's not possible, then to limit the Tx MCS in Windows.
Any insight would be appreciated.

If it depends on the hardware, I have OpenWrt on Tp-links TL-WA801ND, TL-WR1043ND & Archer C7 v2