Even if the FBI created it themselves, still not entrapment, unless they are being prosecuted for using an encrypted messaging app, as opposed to what they said while on it. Now maybe it's a 4th amendment violation, but I doubt that.
Personally, I have no issue with this. What they infiltrated was going to exist regardless. The confidential informer came forward and exposed the business early in its creation, the FBI just made sure that that business was the one that succeeded.
And because it was designed to be used by...