If it's a PON then it's not Ethernet media. You would then be looking for an ONT SFP but those are far from ordinary SFPs. They are not just dumb devices, there is a lot going on inside them since they crammed a whole ONT into the SFP, and it communicates SFI back to the host equipment as if it would have been Ethernet.

https://hack-gpon.org/ont-wo-mac/

You would need the ISP to "adopt" your ONT into their network similar to what is observed with cable modems.