Does the 'thumbnail' manifest property support internal resources url?

I was trying to use internal resources url for the gadget module, but it is not woking. Is it support the internal resources url or there is forge bug?

jira:dashboardGadget:
    - key: bla-bla
      title: Test
      description: Test.
      thumbnail: resource:page-assets;logo.svg

Based on the documentation, I would say that it does not support resources but only full URLs.

Does it mean that my app will not be eligible for RoA if there is a thumbnail on an external domain?

Might depend on the domain name. It seems some are allowed by default: https://developer.atlassian.com/platform/forge/runs-on-atlassian-apps/#remove-egress-urls-that-are-allowed-by-default