I haven't been able to find anything specifically around popup animations, but the BBC's Cape initiative discusses some of the stimulations etc. that can be intrusive for those with neurodivergent conditions such as autism spectrum condition, ADHD, etc.
I've found that most of these chatbots will use sound alerts to draw attention, and Cape's environmental toolkit definitely references these. While a lot of the content in this toolkit is for physical environments, a lot of it will transfer to digital product UX in terms of stimuli etc.