Rough running P301 nd P420 codes

My 2006 prius with ~ 180,000 miles has been having issues with intermittent rough running for a few months, and low power more recently. It throws codes P301 (cylinder 1 misfire) and P420 (cat code). Bought new and has been self maintained. Had a free replacement hybrid battery at 149,000 miles (lucked out there), have never replaced the 12v vehicle battery but it tested good last I checked a few months ago.

Re rough running - I have changed plugs, swapped coils with cylinder 1 and checked all the electrical connections to injectors, coils. Cant find what is causing this - looking for ideas on other things to try. Have run injector cleaner through a few times - wish I had a spare injector set to test or could easily swap injectors but don't think that is possible and cost of new injector rail prohibitive?

The low power seems related to low hybrid battery charge, but also likely related to the rough running.

The P420 code - thinking of changing the A/F ratio sensor (upstream) to see if that might fix the code, but hate to spend $160 or so on a guess.

Recently getting a rattle type sound underneath engine area only under hard acceleration - sounds like metal on metal not like an exhaust leak - checked all the heat shields for tight fastening, condition of exhaust components - nothing externally visible amiss. Rattle is not speed related definitely seems engine rpm related.

Maybe cat is really bad and some pieces inside rattling at high flow rates?

Live in CA so difficult to get a used cat, considering aftermarket and paying someone to cut out the old one and weld in the replacement. Cost of Toyota parts is out of sight and with older high mileage cars hard to swallow.

Anyone with thoughts?
Thanks, Steve