This is kinda shocking. Presumably related to the layoffs. Sounds like they intend to support AB testing natively in GA4 but it doesn't have a release date.
Yes I was surprised too, but if GA4 has a different optimize platform then that would make sense considering how fast they're getting rid of classic Google Analytics.
For them to announce the sunset before they announce the new product has to be a rush decision due to layoffs. That or they just don't believe in this product at all. GA4 has been available for a while and UA still has a while before sunset.