Yes, Apple made it a requirement to be part of the Apple Developer Program for all extension developers. This may have already been part of the Apple ToS or added as they found that any Dev could have their code running on iOS without going through the requirements to do so.
Extension developers were notified of this over the weekend and it will take some time for everything to get back to normal. If all the developers choose to sign up for the ADP
Hope all that helps and makes sense. However I’m saying this from an extension developer stand not twitch