I would expect double dashes ("--") after the first one to be passed through as an argument. A simple test script:
#!/usr/bin/env -S usage bash
#USAGE min_usage_version "2"
#USAGE name "double_dash test"
#USAGE about "Test double dash behavior"
#USAGE arg "<args>..." help="Args" double_dash="automatic"
# echo args
echo "$usage_args"
The behavior appears the same no matter what double_dash behavior is specified. For example:
$ ./double_dash_test -- hello -- goodbye --
hello goodbye
I expect to see hello -- goodbye -- since I would expect everything after the first double dash to be treated as an argument.