1. After re-checking T184214 and talking to @Mattflaschen, it seems that filters for a specific subwiki on Recent changes work as expected. Two search criteria should be entered:the type of wiki and the wiki abbreviation, e.g. 'Wikipedia' and 'mns'.
2. To opt out from Recent Changes new filters, Preferences-Recent changes 'Hide the improved version of Recent Changes' option is used. I checked it specifically for incubator.wikimedia.org and it works.
@C933103 If you still are having some issues with RC filters, you may add your comments here or directly on the task T184214