Two actively developed #foss #linux desktop #RSS GUI readers today: #akregrator and #rssguard (*)
Both are C++/Qt based. Akregator is part of the #KDE collection. It can handle a large number of feeds (>100). It has search but no filtering / tagging capability which is essential if you want to get on top of the information firehose. I have not yet tried rssguard.
(*) A third C++/Qt project was #quiterss. It is currently abandonware with dubious privacy/security status