2013 WRX STI multiple erratic problems since prolonged dead battery during COVID

I have a 2013 WRX STI that has had multiple problems since new. It has always guzzled oil like my 87 GMC pickup with 200K miles. Threw the cam timing belt at 16k miles. The current problem is that it sat for around 2 weeks with a dead battery during COVID. It has had erratic problems since then like barely being able to climb up a small hill immediately afterward. Now it throws various engine codes like random cylinders misfiring, or right or left exhaust manifolds too rich or too lean, etc; Stumbling when accelerating particularly in third gear off and on. It has upgraded Garret Turbo and free-flowing downpipe and Cobb intake. I have changed multiple tune parameters with my Cobb tuner, cleaned mass air sensor and nothing helps. The ECU acts like it is fried but I don't understand how a prolonged dead battery would fry ECU. It ran perfectly before but now driving me crazy trying to figure out what is wrong with the car, particularly with the erratic engine error codes. Some people talk about resetting ECU while others say never reset ECU?