Upload to ATSAMD21J17A Arduino Zero variant fails

[rebgo]

I have created a Arduino Zero variant with a ATSAMD21J17A, and created a bootloader based on the topics Customizing the board def and bootloader for SAMD21G17A and 128k vs 256k ATSAMD21 with SAM_BA_USBCDC_ONLY. The bootloader can be uploaded using openocd and an Atmel-ICE. The LEDBUILDIN pulsates and the Arduino Zero bootloader (COM20) can be found.
When uploading from within Arduino IDE 1.8.19 (with verbose) or Visual Studio Code the following error is shown:

Uploading using selected port: COM20
C:\Users\reb\AppData\Local\Arduino15\packages\arduino\tools\bossac\1.7.0-arduino3/bossac.exe -i -d --port=COM20 -U true -i -e -w -v k:\Work\Firmware\ELAS\ELAS_v1.0\build/main.ino.bin -R

No device found on COM20
Set binary mode
An error occurred while uploading the sketch
readWord(addr=0)=0x20003c00
readWord(addr=0xe000ed00)=0x410cc601
readWord(addr=0x41002018)=0x10010301
version()=v2.0 [Arduino:XYZP] Dec 21 2022 09:44:32
chipId=0x10010001
Unsupported processor
Send auto-baud
Set binary mode
readWord(addr=0)=0x20003c00
readWord(addr=0xe000ed00)=0x410cc601
readWord(addr=0x41002018)=0x10010301
version()=v2.0 [Arduino:XYZP] Dec 21 2022 09:44:32
chipId=0x10010001
Unsupported processor

Why does it mention an unsupported processor? Or what could be the reason the upload fails?

[rebgo]

I found the cause of this problem. The bossac.exe version 1.7.0 as provided with Arduino IDE 1.8.19 simply does not support the SAMD21J17A (ChipId 0x10010001). See also Custom board similar to MKRZERO bossac problems.

The solution is to use a different version of bossac.exe, namely the one from Mattairtech: Version 1.7.0-mattairtech-3 (See also https://www.mattairtech.com/software/arduino/)