Well the title says it all when on WIFI 2.4Ghz the channel width can only be 20Mhz despite the router being at 40MMhz channel width. This effectively halves the internet speed the phone receives.
Issue emerged after the latest OS upgrade to Android 11 that was done in April 2021. Before this, the phone was able to use 40Mhz channel width at 2.4GHZ WIFI.
Sidenote: I have verified that only the Galaxy A70 faces this issue and no other device I have has this problem. Also tried with other routers as well that were on 40Mhz channel width and the problem there persists as well for the A70.