Most sushi fish is indeed frozen at some point, even at fancier places. Unless fish is coming in on a day boat, how else would they keep it from rotting?

Some small local places where the chef can buy fish on the docks everyday might have true fresh fish. Honestly with flash/blast freezing and the like + proper thawing it is unlikely you would notice the difference.

Hence most talk of sushi "freshness" in the US is largely just baseless snobbery...