The 100 strongest amateurs in the world are surely all from the East Asian go powerhouses of China Korea Japan Taiwan. Vast majority of these will be former insei (or yunguseng, or whatever the Chinese call it) who didn’t make pro, maybe a few just studied in a go school but weren’t insei.
If you are talking about top amateurs from other countries, then there’s not many at the top insei level of European 7d+. To take example of Stanislaw Frejlak 7d from Poland who recently beat pro strength Chinese amateur Ma Tianfeng in the WAGC he hasn’t been an insei, but he has studied in a Chinese go school as part of the EGF CEGO training program. Older top European players like Cristian Pop 7d and Csaba Mero 6d did study as insei in Japan (Christian’s friend Catalin Taranu made pro). I know Cornel Burzo 6d is unusual in being one of the top Romanian players who didn’t study as insei.