Pilot reported NMAC with another aircraft while in cruise flight.

Narrative

I (Aircraft X) was on the I-80 Eastbound transition through SLC to continue southbound toward ZZZ. I was descended by SLC TRACON to 6000 ft. to join the transition and was cruising at 6000 ft. for roughly 10 miles before the incident. Aircraft Y finished doing maneuvers around TVY and began intercepting the I-80 eastbound transition for a SLC approach. They were on a climbing right turn from a lower altitude and had a vector collide at my altitude. They were speaking with SLC TRACON; but the controller did not mention any traffic alerts to the aircraft and I had to make an evasive maneuver to avoid the collision. SLC TRACON was talking to Aircraft Y when they were within near midair collision standards and I advised SLC TRACON afterward that I had to make an evasive maneuver to avoid Aircraft Y. I think what caused the incident was that SLC TRACON was busy and Aircraft Y was relying on them for traffic advisories and was not scanning ADS-B or the air for other aircraft as they did not attempt to make any maneuvers to avoid me. I think what should have been done is that SLC TRACON should have given that traffic alert when it was relevant and they were very busy; but they still should have given the alert and Aircraft Y should have still been scanning the air; ADSB-B; ForeFlight; etc. for other traffic.