Is this going to be available soon? I am planning to submit the app for my wiki to Facebook soon and would like to allow users to disconnect their FB account.

It seems that this may be an issue with the Extension Distributor itself as the code in git doesn't include any dependencies (likely so the git repository doesn't have to be updated each time a dependency is, or possibly for licensing). When downloaded, the archive contains the newer version of the library instead of the older version that MW uses. This is also the case with the WSOauth extension.

I should also add that running composer update after installing the extension doesn't fix the problem. As soon as the cache of the RSS feed expires again I get the error and the site is unusable until I disable the plugin. Re-enabling it after the feed info is cached again makes it work until the next time the cache expires.

I did not install this extension via Composer though and the instructions don't say to do so. I simply extracted the directory to the extensions directory and added the appropriate code to LocalSettings.php. The extension itself ships with the newer version of the library and never says anything about needing composer.

It isn't listed in composer.json for that extension at all - it's just included as one of the libraries shipped with that extension. I didn't install it via Composer either. Do I need to rerun composer update after each extension I install?

Further update on this... I talked to a friend who knows a whole lot more about composer and PHP than I do and we tracked down the problem to the GoogleLogin extension, which apparently includes version 2.0 of psr/http-message. Disabling that extension fixes the error, so I will either have to modify my copy of the MWCallbackStream.php file or just not use that extension.

Here is a partial list of composer libraries in my installation (I'm not home at the moment so I can only provide screenshots from the server control panel via my phone)

Return types were added to the psr-message library in version 1.1, per
https://phabricator.wikimedia.org/T335073

Got a similar error to the one MLWatts got when trying to use the RSS extension with MW 1.43.1.