Flight Instructor approaching the VFR pattern reported a NMAC with an enroute VFR aircraft which was not communicating with Tower.

Narrative

During a practice area flight at ZZZ; while descending from 2200 feet to 1200 feet from the ZZZZZ intersection to ZZZZZ1 on the right base for Runway XX; I encountered a near-miss with another aircraft. Approximately 5 miles from the airport and 2.5 miles ENE (East North East) of ZZZ's Class D airspace; while visually scanning and monitoring ADS-B In/Out; I observed an aircraft on a converging path at our 2 o'clock position. We initially detected the aircraft via ADS-B and subsequently confirmed visual contact. Upon realizing the potential for a collision course; I immediately announced to ZZZ Tower that we were on a collision course and required immediate evasive action. I then executed a left-hand turn to avoid the aircraft; which passed behind and below us.The other aircraft likely inbound to ZZZ1 appeared to be monitoring ZZZ Tower but did not broadcast their position or acknowledge our presence.This incident was particularly concerning due to the limited visibility and the converging traffic patterns in the vicinity. The airspace in this area experiences significant traffic density; with aircraft arriving at ZZZ and departing from other airports; creating a challenging environment for maintaining separation. While I understand that right-hand traffic typically has the right-of-way; the late visual acquisition of the other aircraft necessitated immediate evasive action to ensure safety.In clear daylight; this is statistically the hardest time to spot traffic.This incident highlights the importance of constant situational awareness; vigilant traffic scanning; and the judicious use of flight-following services; even for relatively short flights. While I cannot control the actions of other aircraft; this experience underscores the need for proactive measures to enhance safety; such as obtaining flight following for improved traffic advisories and maintaining a sterile cockpit environment to maximize situational awareness.This incident serves as a valuable learning experience; emphasizing the critical importance of constant vigilance; effective communication; and the utilization of all available resources to maintain safe flight operations in busy airspace.Additional notes; I would like to add are; what is fickle about the arrival procedure; is that the lateral bounds of the arrival corridor act like a funnel; where inbound and outbound traffic pass by one another; as other airspaces to the south and north condense the Class E airspace corridor where several aircraft traverse through. Aircraft that head south to other airports while ZZZ arrivals descend through there all of the time is common -- and that airspace is busy as it doesn't allow much wiggle room for opposing traffic to maneuver around one another.In retrospect; the simple answer is to obtain flight following; even if the nature of our flight was approximately 30 min; where we are flying out east briefly; and then returning back to the airport of origin; as more precaution in avoiding that traffic occurs (since there could have been better awareness from not only the pilots but ATC calling out other traffic (hopefully earlier on). Besides the other modalities of traffic collision avoidance that we had at hand; such as our eyes; ADS-B; and tower control; we did the best we could in handling the situation with what services we were utilizing (minus the flight following; which might have ultimately led to a safer more conservative outcome in vectoring around traffic).The training environment can involve lots of talking and division of attention away from looking outside. I teach in briefs ahead of time (such as in passenger; before-flight briefings) sterile cockpit procedures when approaching airport vicinities as we need to look out/not miss other traffic and radio calls. We were silent and vigilantly looking around for traffic during the occurrence; the better factor could have been coordinating with ATC for flight following advisories. Busy airspace necessitates prudent scanning and traffic avoidance (and; if possible; advantages of opting for flight following); and writing this report will help me; and hopefully others; in key takeaways of how to properly be set up for/minimize situations like these.