I've found the root cause.
It's not the driver. It's a regression of an issue in the build configuration.
The 21.02.2 stable build is including the package kmod-mt7663-firmware-sta and as @nbd explained in another discussion here, it should NOT be included in the builds.
The workaround for now is after installing 21.02.2 stable and before enabling the 5Ghz radio, manually remove package kmod-mt7663-firmware-sta and reboot.
After this the 5Ghz radio can be successfully configured and enabled.