2010 Prius Mileage Going Worse

New to me for last 2 weeks - 2010 Prius - 191K Miles approx.

Previous owner has done 5K oil changes, ATF, spark plugs, etc ( I m not aware of when exactly). I do not believe he touched EGR.

100% city driving - most of my trips are 20 miles max or less.

Currently at 33MPG as per dash after fill up and trip reset - I can see in the history that previous owner was getting close to 45 MPG based on previous trips. Has All-Weather tires. For change of ownership - I had to get front shocks and brakes + rotors changed for all 4 wheels. Mechanic mentioned that rear callipers may need to be changed in future.

After the brake change, I was hearing squeaking/grinding noise every time I touched/released brakes first couple mins of driving and then it would go away. Currently not hearing it anymore.

Additional info: Car flashed engine light few days ago - which came up with P0420 in app. I used "Dura Lube Severe Catalytic and Exhaust Treatment" before fill up and reset the code. It has not yet come back, I have driving about 100 miles since reset.

I am NOT mechanically inclined - however I am not afraid of tools - however going through EGR videos they are likely beyond my capabilities atm.

A friend bought a 2010 Prius (approx 175K) with winter tires few days ago - and I drove it on a route that I measured driving my own prius and his car was getting about 50MPG for a few miles I drove after trip reset.

What should I be looking at to get efficiency increased?