We ran into this when we were updated to 2021.1. A recent addition to our integrations mistakenly got flagged as after the update even though it was in place beforehand. We were able to get the code working in Postman, but unable to get the actual integration working. We either had syntax or nonce errors, and following the SuiteAnswers, multiple live support calls & screen share sessions, and enough code going back-and-forth to kill a pony later, NetSuite did revert that integration back to SHA1 required. This partner has finished their SHA256 code, but it took quite some time in order to get it working. I think it's a bad way to see what needs new code, but I'll bet that all our integration partners will know a hell of a lot more after today than they thought they did yesterday.