Same problem every now and then. Samsung is unable to fix the battery drains. Even if they are able to fix, they mess it up in their next updates. This time there is a huge battery drain along with lag. FYI, I'm on the latest August 2021 patch.
what I believe that's your phone so far is an old phone do not expect it will stay forever even if you care battery still battery has to end one-day. try to replace battery or maybe the controller of battery like small chip
