<p>The deployment of 5G networks and the development of next-generation technologies like 6G require broad coverage and high capacity to meet the demands of massive device connectivity, ultra-reliable low-latency communications services, and increased data speeds. To achieve these goals, extensive and reliable signal availability is essential. To enhance coverage and reduce infrastructure costs, intelligent reflecting surfaces (IRS) have emerged as a promising solution over traditional relaying techniques. IRS-based non-orthogonal multiple access (NOMA) has been introduced as a key enabler for future wireless communication systems, providing improved spectral efficiency and coverage. In this work, we focus on an IRS-NOMA communication system and derive accurate closed-form expressions for its outage probability. The analysis incorporates critical factors such as inter-cell interference, imperfect channel state information (CSI), and imperfect successive interference cancellation (SIC), all of which influence system performance. The outage probability is evaluated over Nakagami-<i>m</i> fading channels, where both desired and interfering signals are subject to Nakagami-<i>m</i> fading. We investigate how imperfect CSI, SIC errors, and inter-cell interference impact the outage performance of IRS-NOMA, with results obtained analytically and through simulation. This work focuses on a three-user NOMA scenario, specifically for near, middle, and far users within a given cell, providing insights into the reliability and efficiency of IRS-NOMA systems, particularly in internet of things-driven and other future wireless communication applications. The analysis indicates that imperfections in CSI and SIC have a pronounced negative impact on system performance, especially for users with poorer channel conditions. Additionally, the results show that variations in the Nakagami-<i>m</i> fading parameter and the intensity of interference affect the outage probability differently across near, middle, and far users.</p>