Thank you for your feedback:
About 1.: You can delete feeds (feeds are hosted by Drop Feeds), but not articles, because articles are hosted by the the feed provider not by Drop Feeds, but you can mark them as read (may be I can add an option to hide read articles ?)

About 2.: You have found a bug ;-) I will fix that on a next version -> https://github.com/dauphine-dev/drop-feeds/issues/92 -> it is fixed in Drop Feeds 0.9.3c

Edit:
About 1: Now Drop Feeds 0.9.4 has an option to hide visited articles (the strikethrough eye icon)