Mapping USB keyboard Fn key to Option key with DefaultKeyBinding.dict

I have this usb keyboard and macOS 10.14.6. :

I'm using the file DefaultKeyBinding.dict to remap several keys on a MacBook Pro. Is there a way to specify that my right Fn key has to be bound to the Option key.

I need this since I'm trying to have an Option key on the bottom right zone of the USB keyboard, mimicking the MacBook Pro keyboard.

I'd prefer not to use external tools.

I don't find Modifier keys settings helpful for function keys:

Using Karabiner event, it seems like keystrokes on Fn keys are not detected by the Mac. Can I fix it?

Using Karabiner event, it seems like keystrokes on Fn keys are not detected by the Mac. Can I fix it?

You can’t remap the Fn key as it’s an internal keyboard modifier and not sent to the OS

See this answer from a similar question for full details.

Basically, if a scan code isn’t sent by the keyboard to be received by the OS (and the Fn code isn’t), nothing can be remapped.