don't know if this will be helpful, but if you don't have a particular concept for your island, it's probably a lot less overwhelming to start out by decorating small areas, and then connecting them together.
I was in the same situation as you until I started recreating stuff I saw online. I was inspired by
this reddit post to make an outdoors café, and this super creative
museum gift shop gave me the idea to build a plaza around my museum with stalls holding some one-piece fossils and other science-y stuff (like a microscope or a plasma ball). you can also use some of the Nook Miles items to build a theme park, or even just a regular park. then I came up with the idea of making an outdoors library, and a picnic area situated on the second level of my island, surrounded by nature. so I just kept building these little areas and connecting them together, and that really helped improve the look of my island with relatively little effort.
also, don't feel forced to have a super curated island. I think there's a lot of charm in keeping your island looking natural and even overgrown. I've tried to keep my island looking more like a small town with a few areas of interest than a huge city like some people do, and that has taken a lot of the pressure off (of course, if you want to go for the urban look, that's fine -- but I feel like if you don't know where to start, it's best to leave that idea for later).