The “hot categories” aren’t the best focus, believe it or not. Electronics, apparel, sporting goods, home decor, fashion accessories, are all “hot” but there are tens of thousands of competing products in each. The key is researching deep into sub-categories (like fashion accessories > scarves > pashminas) to find hot-selling products with little competition that you can break into with relatively low procurement (buying or making the goods to sell) costs.
That’s the golden apple that Amazon sellers need to focus on. That research takes time but the selling opportunities are out there. If you want to just dip your toe into Amazon, try retail arbitrage first with the free Amazon seller app for product research. It’s a low-cost way to see how everything works before you try to buy bulk products.