Debugging the ESP32-C6 should be similiar to the S3 and C3 with debug_tool = esp-builtin. So you should have a look at How to use JTAG built-in debugger of the ESP32-S3 in PLATFORMIO and check the basics, e.g. that you see a “USB Jtag/serial debug unit” in your device manager and that you load WinUSB drivers for that using Zadig. Otherwise OpenOCD won’t be able to access it all.
Also, more detailed error messages should be in the “Debug Console” tab in VSCode.
It can also be the case that PlatformIO has not yet updated its Espressif32 OpenOCD packages yet, making it incapable of communicating with the ESP32C6 target. That would need bug report filing in Issues · platformio/platform-espressif32 · GitHub. The current one is 6 months old (PlatformIO Registry).