These steps are curtesy of Ari.

1. Install Visual Studio Code
2. Install Platformio extension in VS Code (press Ctrl + Shift +X to bring up the Extensions window, then search for PlatformIO)
3. Install C/C++ Extension Pack in VS Code (as above)
4. Install Git Extension Pack in VS Code (as above)
5. Install the silabs drivers on your computer (not required for Mac users), such as the “CP210x_Universal_Windows_Driver” (Windows users: there will be a “silabser.inf” file. Right click on this and select “install”)

Now you will (finally) be able to connect the device via USB-C cable and LilyGo's “T-U2T” adapter. Ensure the device shows up in device manager (if not you may be a using bad USB cable - trust me and try different cables). When connected, note the COM port number. In VS Code, click on the PlatformIO icon (looks like a bug/alien head) and choose the option to make a project. Your project name should have no spaces.

The “Board” should be “TTGO T-OI PLUS RISC-V ESP32-C3”. Framework is “Arduino” Then in PlatformIO's platformio.ini file, make sure you have the following:

[env:ttgo-t-oi-plus]
platform = espressif32
board = ttgo-t-oi-plus
framework = arduino
board_build.mcu = esp32c3
board_build.f_cpu = 160000000L
board_build.filesystem = littlefs
upload_speed = 921600
monitor_speed = 115200
lib_ignore = examples
lib_deps =
    https://github.com/Xinyuan-LilyGO/T-ZigBee.git
    bblanchon/ArduinoJson@^6.19.4
    mathertel/OneButton@^2.0.3