Trying to do a full firmware update on Pixel 6 pro after a factory reset (due to hack)

I used a QR code at the mall parking, but instead of paying the toll, it started making a transaction (which my bank immediately caught and cancelled my card). One did get through, so I did a factory reset and did fresh app installs (with nothing from "backup"). Then I changed my passwords.

So nothing identity-wise seems amiss 2 weeks later, but now my phone's battery is dying rapidly. Before this, a charge would last a day or so; now it's lasting a couple of hours before it drops into the teens.

I've seen that because sometimes the hack is hardware level that a factory reset doesn't work but requires a full firmware up date. Tried this with USB debug and adb on computer, but it would connect to my phone.

Any suggestions (for a novice) to fix this?

TIA