The rule since 2020 (when supershoes really started taking over) has been 40mm stack height/1 carbon plate: https://worldathletics.org/news/press-release/modified-rules...

As for training, that's a pretty contentious topic in the running community right now -- some recent research concluded that training in supershoes might actually impair race performance: https://www.outsideonline.com/health/training-performance/su...