Not exactly, the OK AG can still bring claims against solely non-US citizens, but Gorsuch essentially gave a close reading of the Indian treaties which are still in effect, and found that the temporal area they encompassed included half of Oklahoma.

That half of Oklahoma now has to apply a bit more federal common law and probably the court of first review would be federal District Court but that's already currently in place anyway under the general application of federal subject matter jurisdiction.

Thus the operative question would be whether a federal subject matter jurisdiction applies here, and in this case it could arise on questions of whether the defendant is covered under the Indian treaties and whether the underlying case arose on land covered by the Indian treaties.

I hate it, but Gorsuch is right.

If we want to pull land away from the Indians, we need do it openly and clearly otherwise we leave legal timebombs like this which now leaves the entire state of Oklahoma needs to ask whether federalism still exists there.