IPQ40xx devices do not use DSA in 21.02 stable. However, the UCI syntax in /etc/config/network has changed from 21.02 onwards.
Best person to answer this question might be @NoTengoBattery.
You may wish to try his custom build which I recall fully supports VLANs etc.
https://forum.openwrt.org/t/optimized-build-for-ipq40xx-devices/44125