The Nissan Frontier, in its current generation, has been out for a long time now. Given the time frame that this iteration has existed, Nissan has got enough and more time to perfect this mid-size pick-up truck to a point that the complaint numbers have fallen to just single digits. It also has only one recall for the 2019 model year and that too for a minor software glitch that it shares with its siblings. That said, no vehicle is perfect and complaints could show up when they least expected.
Though the number has been on the lower side, there are certain aspects to look out for when getting one of these trucks which have been discussed in detail in this article. The 2019 Nissan Frontier reliability rating of 80/100 is pretty good but falls behind popular trucks like the Chevrolet Colorado, the GMC Canyon, and the Toyota Tacoma. Check out the Youtube video by "MaxTheCarGuy" which lists all the common problems in this generation of the Nissan Frontier.