I've moved this from the Using the Community forum (which is the forum for issues using the forums) to the Lightroom forum so that proper help can be offered.
[moved again by moderator. This belongs in Lightroom Classic, not Lightroom ecosystem]
These are not three catalogs. There is one catalog, which is the .lrcat file. The Previews.lrdata file is a helper file that belongs to the catalog. You should not delete it. The .zip file seems to be a catalog backup. Apparently you let Lightroom made a backup on quit. Making backups is a good idea, but it is better to let Lightroom save them on another disk if possible. You can choose the destination in the backup dialog.
These are not 3 catalogs. Only the .lrcat is a catalog. The other is the previews, which LrC uses, and a .zip file, which I don't know why it is there, probably something you did.
You need the .lrcat file and the previews.lrdata file. I don't think you need the .zip file, but as I said, I don't know why it is there.