It looks like Sneed and Burns both got the exclusive tag and then their teams traded them. This link explains the different tags and toward the bottom it shows who go the exclusive tags and who go the non-exclusive tags (just one guy, Kyle Duggar)
https://operations.nfl.com/updates/the-players/2024-franchise-and-transition-players-named/
But that makes sense, because the Giants and the Titans were willing to pay Burns and Sneed the franchise tender amount, but in the end just negotiated a long term deal instead. So the Vikings might be able to find a trade partner who doesn't want to pay him 41M, but is willing to negotiate a long term deal, but will they be able to get Darnold to play ball? He probably shouldn't play ball and refuse to negotiate with the team of the Vikings choice, because if the Vikings are forced to let him walk free, he can negotiate with any team, picking his own destination and likely getting more money.
I think the transition tag is the same thing as the non-exclusive tag.