A significant number of Google users on forums report that their Pixel 6 won’t charge through certain chargers and cables, despite the fact that everything works fine with other smartphones.
It seems that the reason for the incompatibility lies in the quality of the cable and charger. These are products that do not comply with the USB Power Delivery standard. These were probably cheap devices.
It’s worth noting that this is not unexpected behavior. Google’s support page says Pixel phones “may not work” with some cables. This is most likely to protect the battery from potential damage from slow chargers or cables that do not meet the USB-C specification.