Commercial Fixed Wing
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 14
Communication Breakdown; Workload
ATC Issue All Types; Conflict NMAC
Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification
Airspace Structure; Human Factors; Procedure
While working Flight X inbound to ZZZ who was descending on the RNAV Arrival I observed a VFR target merging. I issued traffic approximately ten miles away. Flight X was level at 12;000 ft. while the VFR Target appeared to be at 14;500 ft. The target in question appeared to be descending toward Aircraft X; so I issued a direct descent to 8;000 ft. for Aircraft X. The VFR target also began to descend. The only turn that would've worked in my estimation was a left turn; but that would have put Aircraft X in another unsafe position with terrain/Minimum Vectoring Altitude (9500 ft.). A right turn would have been converging and earlier descent could have cause loss of radio communication and RADAR coverage. I reported the incident to the Operational Supervisor in charge immediately and was just informed today that the crew of Aircraft X filed a NMAC report. I honestly don't know what could have been done. My understanding is that the conflicting aircraft canceled an IFR flight plan to ZZZ1. Perhaps had I been speaking to that aircraft; this could have been avoided. There was really no good alternative or course of action in my opinion.
TRACON Controller reported an Air Carrier descending on an RNAV arrival reported a NMAC with an unidentified VFR aircraft.