No, that's my understanding as well.

My fiber installer referred to the Adtran 632V ONT he installed as the "modem".

He installed two other junction boxes (one outside the house near/under where the fiber attaches to the wall of the house, one inside near the ONT) but they're just passive optical couplers allowing them to swap out fiber segments in the event of fiber damage without re-running the entire install.

Can’t speak to this exact circumstance, but more generally: The ONT translates the SFP+ networking to fibre optic, but the modem is still somewhat necessary for logins if you use PPPoE as a wrapper for example. In telecom fibre optic, it often also assigns a particular vlan to internet packets and separate vlans for TV and phone. But I’m not an expert here, just explaining why I needed a modem function in my router as well as a media converter to house the ONT.

As far as I know, nobody uses separate boxes for the modem and router, that kind of thinking died when wifi became more widespread and included by default with ISP plans.