I don’t know about that. As far as I remember it wasn’t a big rumor before very shortly before the pick was made.
I have found a video (click
here to see it) of Adam Schefter on draftday saying “there’s a growing belief” that the Browns could take Mayfield. Or there’s this tweet from Ian Rapaport (click
here) the same day stating “[Mayfield going #1] is the buzz…”
Then there’s this tweet (click
here) on draftnight from Benjamin Allbright (who, by the way, someone recently brought up as a highly trustworthy source who says that Kyler Murray to the Cards are a done deal): If I were a Browns fan, I'd start prepping for Mayfield. I was wrong on Darnold.”
There’s also this quote “Kiper previously had QB Josh Allen going to Cleveland in
every one of his mock drafts, so he made the concession for Mayfield based on all of the reports today.” Or Todd McShay from his mock draft on draftnight: “I’ve had Darnold here in every mock I’ve done, dating back to my Way-Too-Early mock in May 2017, so why waver now?” (Click
here to read the article)
Speaking of Allen to the Browns I think you are wrong as well.
Other than the quote from Kiper, there’s this quote from Pete Prisco of SI.com on April 12th (click
here to read the article): "I think [Allen’s] going first overall," Prisco said. "I hear that too much from guys I respect in the business, who know a lot of people in the business. I'm talking about scouts and personnel people, who know guys and know Dorsey. I just keep hearing -- I've been saying it for a long time, and I just keep hearing it more and more that he will be the guy who goes No. 1 overall when it's all said and done." A couple of days earlier came this tweet (click
here) quoting Daniel Jeremiah saying: “people that know people inside the Browns fully expect Josh Allen to be the pick at No.1.”
You see where this is going?