Is there something specific you are referring to? I haven't played any of the non-Nintendo Switch 2 ports, but the reviews haven't suggested widespread performance problems.
What is true is that (for example) Split Fiction and Tony Hawk 3/4 are quite a bit less fancy than the PS5 or XBox versions, which is unflattering.
People have been saying the Elden Ring port is looking to be a dog.
I have read that too (particularly in handheld mode) but Elden Ring is a bit of a dog on PC and PS5, this might not be the best example. The engine has way too much cruft to ever run smoothly.