I had limited time, skills and experience when I first started investing. Like many here, learning about Buffett and Berkshire just resonated. The rationality, downside protection and internal diversity made it the standard against which any other capital allocation was judged. I knew I was dumber than Buffett and just piled on whenever it seemed relatively cheap. Was up to 90% at one time. But Berkshire is unique and it is the only security I'd ever recommend to someone who asked. (because of that downside protection- the quote might get cut in half but the businesses....) Would that work for a new investor now? Hard to say with Buffett unlikely to be at the wheel for a new person's horizon.
That said, in an area where you have special expertise and you see an opportunity, why not dive in? what good will it do you to invest by the teaspoon if you truly have a good idea? Trouble is, new investors seldom really have special expertise. I happened to sell my little business toward the start of the pandemic. We were having a spectacular season of sales. Took the proceeds and invested in a public company in the same line of business. Kept the concentration even after the stock popped because I have long experience in the industry and feel comfortable with the future. But with most areas, the future is full of perils and you really have to have LUCK on your side.