i wouldn't recommend you to downgrade. Your battery life is most probably effected because of alot of useless data (duplicate file , large file) or apps are running in background. Try enabling "Kill background apps" from developer option. This worked...
these security patches dont contain any features. It only inhances security of your device and removes bugs if there are any. All the major update will come when you update from android 9 to 10.
its going to take a while because android 10 beta version just launched in korea. Then it will come to US then hopefully its beta version will come to pakistan as well.
