Thank you very much for taking your time for this.
From your information, it seems the bossac has "-o" options in source code, but does not have in binary execution code.
> I would try compiling bossac from source trying that version. Please
> consider filing a bug against the Zephyr SDK about the missing option if
> that solves your issue.
I will see.
From your information again, it seems the Adafruit Trinket M0 is unmaintained. Updating the SDK somehow broke the condition to compile and flash the Trinket M0 in current SDK version.
I will check how to solve this.