The plugin brings the excellent CopyParty, which is a file server program. After toggling it on from the Decky plugin, you can go to the provided IP address on any of your devices, enter the password, and access the Deck’s files. You can manage files, upload or download files, and more. File transfer speeds are fast and resumable.
Here’s the GitHub for the plugin, although for right now it’s pretty bare on a description. For details one what all it can do, I’d recommend checking out the CopyParty link up above.
I ssh into it with my file browser “Dolphin” on Linux (the same that is used in the Steam Deck as well). Needs to be setup first, but then I can access the files with the file browser. And secondary I ssh into it in terminal, but that is not to transfer files, but to have access to commands execution on the device (like installing something from commandline).