I've been on the same search for a program. I think the one Debbie recommended, Scrivener, is still the tried and tested app with the most and most useful features. I'm not a computer person though, so it's a little too much and a little too intimidating. The layout isn't intuitive or aesthetically great. But if you're looking for functionality, Scrivener does all the things.
If you have a Mac, Vellum does most everything Scrivener does in a more intuitive, aesthetically pleasing way.
WordPerfect does a lot of what the above two do, but since it's not specifically for book writing, it can be a pain to find youtube tutorials on what you're looking for.
If you have any kind of ADD, dyslexia, dysgraphia or just trouble focusing, IA Writer looks to be a great program. It has several features like "focus mode" that look to be based on dyslexia research I've seen. Very minimalist, useful features, not exactly aesthetically great. I might still switch to this for the focus mode, it looks like a great program. https://ia.net/writer
Currently I'm trying Shaxpir. It has a free 30 day trial for the pro version and I think I'm likely to stick to it. It doesn't have a lot of features, the search feature is not great and I have to C&P my chapters into Word (and match formatting) before C&Ping them here, but other than that, it works for me. It's the most aesthetically pleasing of the programs I've seen (I like the default, but there are several themes to choose from if you want something akin to Reddit's dark mode). It keeps things in book format while you're writing and has your folders and chapters on the sidebar constantly, which is really all I wanted. An added bonus for me is that it doesn't spellcheck unless you want it too. I really hate Word telling me what to do with its squiggles. I'm sure there's a way to turn it off, but I'm computer lazy. If a feature isn't intuitive, I don't like going out to hunt for it. Though if you need a spellchecker... well you might want to skip Shaxpir. A brief test showed its internal dictionary to be not very inclusive. It told me "curtly" wasn't a word. So there's that. Granted, Word's isn't great either. I'm unsure why they don't just check these internal dictionaries against Webster and Oxford to make sure they've got the most of everything. Anyway, all I wanted/needed was an intuitive, aesthetically pleasing way to get organized as opposed to having 5+ Word windows open constantly. This is effortless organization, but if you're looking for more, you'll be disappointed.
The conclusion is, it really depends on what you're looking for.