i live in germany and to me telegram doesn't feel niche at all.

a lot of younger people use it a bit like discord, like for group stuff. organizing (like e.g. political activism), finding apartents in berlin, and yes, getting drugs as well. also some worklplaces use it (which i think is terrible). it is also preferred by a lot of people to communicate via telegram over signal or whatsapp in situations where people don't want to give away their number, like online dating.