

So everyone else has good points but there’s one other part I don’t think was mentioned.
Most ISPs use a PON based network. This lets them connect one fiber in their network and “split” that to up to 128 (or more, depends on the OEM) customers. You need a either GPON (Gigabit passive optical network) or XGS-PON (10 gigabit symmetrical passive optical network) SFP module and usually the ISP has to get a serial number off of that module to provision the proper data service.
This is contingent upon the ISP being willing to do that. The one I currently work for, we really don’t do that except for businesses.

You cannot just buy any SFP module and have it work. Most ISPs deploy a “special” (at least compared to normal point to point fiber links) that lets them serve multiple customers out of one port in their office. This is called a Passive Optical Network and requires specialized modules on both ends. There are ways to make a specific SFP work as an ONT and by cloning certain identifiers from the ONT to make the ISP think their box is still there.
This is a lot of effort and from my research, could stop working randomly in some cases.