While working on #4661, we noticed that the introspection framework doesn't read the includeDeprecated flag, which selects (or not) fields and/or enum values which have been deprecated. Although #4661 does add support for deprecated enum values (thus no longer exposing them through introspection unless explicitly requested), it does not add this support for deprecated object and interface fields, as this would require significant work. @0x777 commented:

If we were to fix handling includeDeprecated argument correctly, the deprecation information in case of fields for object types introduced through remote schemas has to be propagated from the introspection query.

We should add support for tracking deprecation of fields of object and interface types, and consequently use this information in the introspection framework.