My inspiration usually comes from the mix of stuff I grew up with (fairy tales, history, video games, etc.). Some Google pictures and ACNH speed builds I watched (really satisfying watching those builds). Throw in the vaporwave, mallsoft, and Japanese city pop music I listened from time to time into the mix.
It varies from real world formations/structures, video game locations, and ancient history. I'll use Google images for most of my references and the Japanese players I follow on Twitter. If I do take inspiration from other players, I'll try to reimagine the build than straight out copying it. I like to try to put my own twist on it.
From areas I know from real life and from games. I modeled most of my island after shops and landmarks in my home city. Then I also have areas or designs inspired by salmon run from Splatoon. When it comes to shop designs and whatnot, I like to take general build inspiration from what I find online, but try to tweak it to make it my own.
Usually looking at other people's islands and of course trying to be original. I don't really have a theme for my island its just a simple idea with stuff that reminds me of my childhood memories.
I love watching speed builds, they were actually what got me back into playing new horizons. Other than that, real life locale, landscape/architectural art and photography (usually from social media), and other games!
Instagram is good for inspiration, though I often find the people on there to be insufferable. I prefer twitter so far, though there are obviously less pics. I just find walls of text lecturing about how terrible someone else is for allegedly copying their ideas to be unneccesary, which I've seen a lot of on the gram.
I look through Pinterest and watch some TikToks of builds. YouTube is a good place too.
I mostly stick to a theme and look for creators from there. It definitely helps.
You know, I'm probably the community grandma, lol, and one of the reasons I first started animal crossing long long ago was to simulate a place I wanted to move. One of my children suggested it back when it first made it's debut. I've been trying to physically get there for years but finances and life happens. So, I still build the house I dream about retiring in by the sea in every game. I go there like it's my second home.
One day, I'll really get there.