I upgraded to 0.18.4 on Ubuntu Linux.
After the upgrade, my RSS feeds are gone.
How do I get my feeds back?
Where did they go?
Did the database upgrade wipe out my feeds?
look for a file feeds.db in your user home.
For the future I recommend to backup the files feeds.db and QuiteRSS.ini before performing an update.
You can also create an OPML file holding your subscriptions under File -> Export feeds... .
Most likely you have updated from version 0.17.7 to version 0.18.4
In Qt5, the paths to user data have changed.
You need to transfer the files feeds.db and quiterss.ini to the new directory.
The path to the new directory: Menu - Help - About - Information