No automated mod manager
Core Keeper doesn't have a Mods tab with a workshop browser on Spawnly. Unlike games such as Squad or Unturned, there's no in-app browser reading from a Steam Workshop content folder — mod support for Core Keeper's dedicated server isn't something Spawnly automates today.
Be honest about the gap
There's no verified, dedicated-server mod-loading procedure for Core Keeper on this platform. The File Manager (Files tab) gives you full access to your server's directory, so you technically can upload files into it — but without a confirmed mod loader or launch flag, there's no documented way to guarantee a mod you upload will actually be picked up by the server process. Treat this as advanced, experimental territory rather than a supported install path.
If you want to experiment, back up your server first — see Managing Backups & Restoring Your Server — so a failed attempt doesn't put your world save at risk.
Next steps
For branch selection and general setup, see Getting Started with Your Core Keeper Server.