A great gift for a new born baby boy from his uncle is something interactive - baby toys and books of your choice. Pick a subject or multiple subjects that interest you and that you want to pursue with your nephew and get him infant toys or books or both that relate to those themes so that when you visit you can use the gift or gifts to bond with him and build a relationship with him.
For example, if you love sports, buy him his first baby baseball toy rattle. We like organic baby toys because they have less chemicals and are better for baby's tender skin and unlike plastic rattles will not hurt baby if it falls on them. Not only can his parents can use it to interact with him in your absence, but you can get one yourself and use it to engage with him over video calls and of course when you visit or he visits you. As he gets older you can nurture the interest and hopefully eventually bond with him over your joint love of sports - play together perhaps watch him play and watch games together.
And while sports is the stereotypical example, it of course need not be sports at all. If your interest is in cooking, clothes, aircrafts, feminism or something else, you can get him a books or rattle toys that relate to the subject. The key is time spent together and finding ways to foster a bond with your nephew when you're able to see him and when you are apart.
Of course there are other great gifts that an uncle can get his nephew. You can solve problems for your nephew and that could be crucial depending on the circumstances. For example buying him a crib, stroller or somehow defraying the cost of having a baby for your brother or sister and their partner could be great especially if finances are an issue. Further, putting money aside for them through one of many programs for their future education could be fantastic.
The sky is the limit to what you can do for your new nephew. If you have kids of your own, you can pass down to him books, clothing and favorite toys that your kids have outgrown. Not only does this save money and recycle, but your nephew might take pride in owning them. Given the relationship, such hand me downs take on a new meaning and become more loved because it comes from their older cousins.
While there are many great things an uncle can buy for his new born nephew, we love the gift of time. Finding books and toys that he can use to develop a genuine and lifelong relationship with his new nephew. Gifts that introduce the newborn to subjects that are meaningful to the uncle. Hopefully, the new baby can grow up sharing the uncle's passion for sports, cooking, wildlife etc, but if not, they can spend quality time and get to know one another in a meaningful way.