Judging by the code, it filters the routes of nuxt, and not the final xml file data. In my case it does not work. Can you fix this and filter the final data?
As explain in the README, the exclude parameter is only for the static routes generated by Nuxt (see https://nuxtjs.org/guide/routing#basic-routes).
Else you can use the filter parameter to filter the any data before the sitemap generation.
Can you be more explicit about your need? (eg. give an example of use case)