Your installed package metadata is out of date relative to your API version. The activateRSS key is required in InstalledPackage metadata post API version 43.0; see the Metadata API reference.
You can manually add this key to the XML source of the installedPackage-meta.xml files.
Metadata API Settings entities won't ...
Few challenges which I encountered during the upgrading of a package for picklist:
New Picklist Value does not get added.
Change in default Picklist Value.
The only solution is, either the post-deployment activity or reinstalling the package, Or have some scripting logic that automatically does for you.
I also faced the same challenges with : Field ...