The example PlatformIO project with Arduino framework.
The bootloader can be uploaded to the Atmega16 using: Arduino IDE + MightyCore + USBasp/arduinoISP
NOTE: The C2 capacitor (connected to the reset pin) should be removed
Just upload a compiled program, such as the standard Arduino code. Please be sure about "board_build.f_cpu" param in the platformio.ini file.