Boards like the ESP32-C6, almost 5 years old, are not supported in PlatformIO with Arduino libraries, because they refuse to update the Arduino core in some kind of stand-off with Espressif. This has been going on for years. There is a fork [1] that offers support but none of it makes back upstream.

As a hobbyist I've given up on PIO and moved to a barebones arduino-cli setup instead. Much lighter and less painful.

[1] https://github.com/pioarduino/platform-espressif32