I used shared links (RSS) constantly with Safari at Mac and iOS, but after iOS was updated to iOS 11, Shared Links disappeared both in the iOS Safari and in the MacOs Safari (that was not updated - High Sierra will released only 25 of september).
So I could not make shared links sources backup for using with alternate app. And don't remember all sources.
But found a solution for Mac users.
Just start MacOS Terminal App and run next command
=== start of the command===
awk '/FeedURL/ { getline; print $0; }' Library/Safari/WebFeedSources.plist | sed 's/<string>//g' | sed 's/<\/string>//g' | sort | uniq > Documents/MyExportedFeedURLs.txt
=== end of the command (must be one line) ===
Then we can get new file MyExportedFeedURLs.txt from Documents folder and use it to setup new RSS reader app (I tested today some and chose Inoreader)