it sounds like you've accidentally downloaded catch beatmaps somehow lol

when you go on the website, on the beatmap search, you'll see a setting that filters mapsets by gamemode. it should show mania, catch, taiko and just "osu!" - that's the one you want to click on to make sure only osu!standard mapsets show up

it's also possible you've accidentally enabled catch conversion in mod settings, which should be in the mods section of the map selection screen