I’m pretty sure that 95% of the positive responses to this thread are people that are conflating the two, and 4% are people overstating the utter importance of running your own ONT, conflating “it sounds fun for a select few mega-nerds and we should regulate for that” with “meaningful consumer choice”.
Yes. Several ISPs I've used sent out routers with integrated fiber connectors, no separate ONT. Their routers weren't terrible enough for me to want to replace them immediately, but not everybody gets a ONT+router combo from their ISP.
I think it's often more a "router with ONT built in" rather than an "ONT with router built in".