Mt7615e & mu-mimo

Hello. I have an MT7621 router with MT7615E 5Ghz radio and a recent Openwrt snapshot (Redmi AC2100) and I've noticed that it only advertises SU-MIMO and it doesn't seem to be working (I see speed reduced when another Wave 2 device is using the same network). Is it supported by MT76 under OpenWRT (it seems to be working on ath10k Archer C6, so it is should be supported by OpenWRT ?) and if so, how can I get it working?