There is a guide on the terraria forums at https://forums.terraria.org/index.php?threads/terrariadepotdownloader-downgrade-to-any-version.107519/

You can also find it by searching for terraria depot downloader.

That sounds like speedkills. Those likely won’t be added as categories due to their differences from speedrunning. Additionally, I believe most bosses have been optimized down to single frames, and so wouldn’t be very competitive.

Eye of Cthulhu is already a category—check the Individual Levels on the main Terraria boards.