[24255] Consider external members as not plain

[MiguelCompany]

Description

This is a manual backport of #562 to 4.2.x

Contributor Checklist

• Commit messages follow the project guidelines.
• N/A: Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A: New feature has been documented/Current behavior is correctly described in the documentation.
• N/A: Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• Check CI results: changes do not issue any warning.
• Check CI results: failing tests are unrelated with the changes.