The term "511" in this context is likely a keyword truncation of version number 5.11.x. Search engine optimization (SEO) strategies employed by third-party APK sites often capture these specific version queries.
Every major YouTube Studio update introduces bugs—broken upload progress bars, notification errors, or crashes on specific Android skins (MIUI, One UI, etc.). For creators who rely on the app for daily management, going back to a stable build like 511 is a tempting risk management strategy. yt studio 511 version apk