Kermir Battery gets to around 20% then dies quick and just shuts my phone down. When trying to boot back up the battery is at 0% and puts me into a boot loop.
A battery that crashes from 20% down to 0% is worn out, and may well get worse. It might be time to replace it... or, perhaps, to struggle onward until it's possible to replace the device. GrapheneOS support for the Pixel 6 will probably end in a little bit more than a year (source).