FWIW I had a similar problem with some earlier Android devices that had miniUSB jacks. I solved the problem by finding "power only" cables that had two large wires for power, instead of four smaller wires for data and power. Without the data pair there was no way that my phone could detect a USB data connection.
You can't do this with USB-C because it's a 2-way power system that uses the data pair to negotiate direction of power delivery, voltage and current limits. For whatever reason, your phone is detecting something on the data pair that it interprets as USB data and not power delivery-related signals. I'd try a different USB-C power source & cable to see if that makes a difference. To date I've never used my factory AC adapter or cable that came with my Pixel 3 XL, and haven't had any problems using a wide variety of power sources and cables. If you're having this problem with factory Google parts, chances are that one or more of them have gone bad. At least today USB-C stuff is a lot cheaper than when I started buying it.