Feeder is a perfectly functional RSS reader for Android, and the only updated and straight forward one on F-Droid when I decided to set up my feeds, and an app I've seen suggested on Lemmy several times when there's mention of RSS...~~but why doesn't it have groups? I've got my general news mixed with tech news, cluttered in between the rest of it~~ - it does have grouping and it's called "tags"
this thread made me re-check and there are some new options in there and at least one will let you group the feeds: Read You
EDIT: dumb take
there is a fork with proprietary dependencies removed called Signal-FOSS, whose repo you can add to F-Droid if you decide to trust it