I'm using the same MT7921 in an M.2 card running in x86 ... The card only see one of the radios, not sure how to have simultaneously 2 or 3 radios (if 6GHz is working). Also the other problem is that the card only comes up in AP mode if I do "disable and then enable" after a boot. Someone got it solved?
cat /etc/config/wireless
config wifi-device 'radio0'
option type 'mac80211'
option path 'pci0000:00/0000:00:10.0'
option channel '36'
option band '5g'
option htmode 'HE80'
config wifi-iface 'default_radio0'
option device 'radio0'
option network 'lan'
option mode 'ap'
option ssid 'OpenWrt'
option encryption 'none'