Hi, From my side I have only uploaded the firmware directly from the Arduini IDE, and it seems to work fine. I have generated the hex files, and they are also smaller than the original. Perhaps this ...

Alternate option for hex file upload Instead of using arduino-cli, you can also use teensy_loader_cli. This alternative is best if you are running on a headless machine / SBC and using SSH.

A few weeks ago, we saw codebender, an online replacement for the Arduino IDE that allowed you to upload a sketch to your board from a web browser.