boards.local.txt file ignored

[K7MDL2]

This is something to look at for Arduino IDE 2.0 support.
USB types are defined boards.txt along with many other parameters. Boards.txt are supplied in the board packages. Boards.local.txt provides a way to add or override boards.txt entries without changing the distributed version per the Arduino specs.
https://arduino.github.io/arduino-cli/0.29/platform-specification/#boardslocaltxt

As of today, only boards.txt is processed, boards.local.txt is ignored. Arduino 2.0 IDE handles the .local.txt file properly assuming you clear the cached info.

For example, if I add my 3 lines of custom USB Type serial entries from boards.local.txt to boards.txt, the VS Code board manager USB Type menu will show and use the new USB type.

teensy41.menu.usb.serialserialaudio=Serial + Serial + Audio
teensy41.menu.usb.serialserialaudio.build.usbtype=USB_SERIAL_SERIAL_AUDIO
teensy41.menu.usb.serialserialaudio.upload_port.usbtype=USB_SERIAL_SERIAL_AUDIO

Adding these 3 lines will result in the Serial + Serial +Audio USB type to appear in the USB Type menu. Of course, to use it you must have matching section in usb_desc.h file, but that part is out of scope here.

The same local.txt file feature exists for some other config files like platform.txt.

[K7MDL2]

Verified this is still an issue with Arduino extension v0.6.230727001.

Arduino IDE 2.21, TeensyDuino 0.59.3 read the boards.local.txt file correctly.