After all, the US has plenty of instrument approaches outside controlled airspace
Yes, lots of untowered fields have IAPs with Class G at the surface, Class E above 700ft AGL. Centre will separate IFR planes procedurally. Only one on the approach and nobody else cleared until the first one cancels IFR, no departures either until IFR inbounds have cancel. Also when clearance void times are used a lot.
If its VMC then it's see and avoid. Everybody talks on the common frequency. There are untowered fields with IFR wide bodied jets coming in with VFR spamcans in the pattern, all talking on common frequency, avoiding each other visually. I am sure the jet is grateful almost everybody in the States squawks mode C.