Fact is that heads rolled when a Gotland - and on another occasion a German sub as well - penetrated the US carrier group's escort shield in the past. When a German sub once shot fireworks at a carrier after it took photos and then surfaced beside a carrier in closest vicinity to it, the Admiral onboard was said to have "exploded".
More meaningful may be the fact that the US Navy "leased" a Swedish Gotland some years ago that participated in some excercise, with results from those exercises that rang alarm bells in America, and so they asked the Swedes whether they would stay for longer time, to test their procedures and technology against it - and that was not the usual ,military excercise context anymore, that was about cracking that Swedish bug open. But they couldn't. Thje boat stayed first for some months and then for over one year, as a training partner - because they were unable to find it and the Gotland raced circles around its hunters at will. Last report I read somewhere about it was that the Americans were anything but happy.
The worries weigh heavy when imagining such a boat in the hands of a real enemy, or rogue nation.
The Swedes however are smirking until today about it,

saying that the Us observers they took on their boat were "sweating blood" when seeing how chnceless the US units were in trying to find it. As far as I know the Gotland was not detected and intercepted a single time when being hunted, and achieved all its attack objectives in training, sinking them all. That was once reported on some English navy technology website, maybe two years ago.
The German boats are that good that the Americans once
tried to buy the whole German shipbuilding company to get their hands on the blueprints and to prevent the Germans to sell the technology to customers maybe that the US would not welcome to have such boats.
Conventional boats with these new fuel cells and comparable concepts simply are more silent than nuclear boats. The Gotlands and 212s/214s have the reputation to be "undetectable" currently. For best nuclear boats, ask the Brits and Americans. For best non-nuclear boats, ask the Germans, Dutch and Swedes.