iOS / ipadOS app with share action for SCP / SFTP? I've tried a few clients that come up with a search, notably

WebSSH
SCP Client
FTPManager

All of which have the basic functionality of transferring stored files from the Files app, but from my testing none of these have implemented a the share action (i.e. it's not an option when you click the share button and you're presented with AirDrop, Messages, Mail, etc.). Do any of the other apps out there have this?
You can SFTP using iOS Shortcuts app.

Shortcuts can take input from a share action.
Shortcuts has an action ‘Run Script Over SSH’ and passes action input to stdin.
You can cat stdin to a file on the destination.