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Engine code P0420 Bank 1

Is this a sensor(s) and/or the catalytic converter that needs replacement?

Probably, but you should follow the troubleshooting flowchart for that code for your car to be certain before throwing parts at it.

Try the O2 sensor(s) first. They are much less expensive than a new cat. There should be a trouble-shooting procedure accompanying the explanation for this code. Follow the procedure.