Imho this is not at all related to umbrellas, but it’s a problem of library architecture. Even without an umbrella there might be a need to have different configuration to be used with a library. This is never supported when the only way to supply configuration is via the app env.

For scrivener_html this is not a problem though because you can supply config as a parameter:

# MyAppWeb.ex
def scrivener_config do
  Application.get_env(:my_app, :scrivener_html, [])
end

# In a view
import Scrivener.HTML
pagination_links @conn, @page, [], MyAppWeb.scrivener_config()

# MyOtherAppWeb.ex
def scrivener_config do
  Application.get_env(:my_other_app, :scrivener_html, [])
end

# In a view
import Scrivener.HTML
pagination_links @conn, @page, [], MyOtherAppWeb.scrivener_config()

One short function and one is no longer dependent on how scrivener_html does load config and it would work just as well if the issue is not two apps in an umbrella, but rather a “small width” pagination vs. a “wide” pagination.