I’m not sure what’s actually wrong, or what works differently. I am sure that once I set the pin to be a digital pin, the 18B20 code started working. I must have looked at a hundred examples, and specifically ignored arduino (the non esp ones), and none of them set the data pin first. What gave me a clue was one person out there accidentally put the pin mode in when he first wrote the code, didn’t take it out, and it worked for him with the one library he could actually get to compile without errors.
It would seem that the xiao esp32C6 has some differences that the various libraries haven’t caught up to yet. Hence the compilation problems and fixes that haven’t made it into Arduino IDE yet.
I just stumbled into that and was fortunate enough to run across another person that had the same thing happen.