Picard intentionally destroyed all records of the Iconian's technology including the gateway, the probes and all of their own scans.
PICARD: (handing the tricorder to Worf) Destroy this.
WORF: But, sir, it contains the record of all that we have discovered here.
PICARD: And that is precisely why it must be destroyed. Time?
WORF: Three minutes.
PICARD: (to himself) I am running out of time. We all are.
Picard kneels beside Data and pulls him up until the android is
supported against his shoulder. Worf lays the tricorder on the floor
of the chamber and fires his phaser at it. The tricorder VANISHES.
PICARD: (continuing) This room and the technology contained in it must be destroyed. It cannot be allowed to fall into Romulan hands.
TNG: Contagion - Original Screenplay
What remains are simply the recollections of the crew, little better than broad descriptions of a technology that's so far in advance of the Federation's that it might as well just be magic. We can assume that the post-mission debrief went something like this...
Federation Scientist: So, Captain Picard, can you please describe the Iconian
Gateway in as much detail as possible.
Picard: It was a sort of glowing window thing that went places.
Federation Scientist: OK. Thanks for that. Very useful.
As regards any scans taken of the second Iconian Gateway seen in DS9: To the Death, based on Worf's account of the previous mission, and noting Starfleet's approval of Picard's decision to destroy all data about the Iconian Gateway, it seems very likely they would have done the same with any readings taken on that gateway, even had it not had a dampening field around it preventing closer inspection.
WORF: I was on the mission that discovered the Iconian homeworld. We were forced to destroy the Gateway we found there rather than let it fall into Romulan hands, and Starfleet Command supported our decision.
DS9: To the Death - Original Screenplay
That being said, it doesn't stop rumours from spreading...
PARIS: If it'll make you feel any better, I'll let you in on a little secret. I was on the bridge this morning when we received a
hail from an Iconian scientist. He claims to have a trans-dimensional
gateway that can take us anywhere in the galaxy.
KIM: I'm not that gullible.
Voy: Inside Man