Just for info. the new Fritzbox 5530 fibre has a built in ONT. Don't know if available in or work with the UK system.
Yes there’s many consumer level routers that now have SFP ports or indeed GPON ONT transceivers built-in, but it’s not really a plug and play operation (for end users) with the GPON nets here in the UK.
We have several dozen AltNet’s and the incumbent, Openreach, all of which supply and support their own flavours and mix ONT or ONT/router manufacturer equipment, rolled in, fully supplied and supported as part of the overall service.
Supplying your own ONT is not really the done thing here - unless you’re into the curious, weird, wacky and experimental. Even then there’s no guarantee it will work and in any event the service provider will take a dim view of anyone that tries and messes up their connection and potentially affects other customers on the PON.