Cannot enable any UART other then default

Troubleshooting
2

I gathered some info from this post

  • Enable serial console with dietpi-config should already do all steps for you, but to be sure:
  • Verify that /DietPi/config.txt contains the line enable_uart=1.
    Verify that /DietPi/dietpi.txt contains the line CONFIG_SERIAL_CONSOLE_ENABLE=1.
  • NEVER do systemctl disable getty@tty1.service as TTY1 is always needed as fallback

Important when using UART devices for something else then a serial login console, is that you disable serial console usage. On DietPi do:
dietpi-config > Advanced Options > Serial/UART