file browse:

https://example.com {
        root * "/path/to/dir"
        file_server
}

file browse: grid default/forced view

https://example.com {
    root * "/path/to/dir"
    file_server browse

    @directories `path('*/') && {query} == ''`
        redir @directories ?layout=grid
}

reverse proxy:

https://example.com {
        reverse_proxy 192.168.1.123:8080
}