Gotta be a trade or extension. If they are working on a free agent right now they'll get hit with tampering. I don't think they can even have conversations with FA agents for another week or so.
Trade for a WR seems to be the most obvious answer.
Could also be a more expected move like an extension for Dak, Lamb, or Diggs.
A Diggs trade cant be 100% ruled out, but I'm guessing that's doubtful.
Longshot answer but I like to stir the pot would be a Dak move for a top pick this year to go get CJ Stroud who they have been oddly linked to.