Redditor "u/PraiseHolo" stated in a guide flair that the furniture in Animal Crossing's Nook Stop is not randomized. In the guide flair, "u/PraiseHolo color-coded the furniture in Animal Crossing's Nook Stop. The first four colored folders are furniture from the four airports in Animal Crossing: Blue Airport, Orange Airport, Green Airport, and Yellow Airport.

All Airport folders consist of the same items: a street lamp, a solar panel, a wind turbine, a utility pole, a big vending machine, a Godzilla-like dinosaur, a colorful teacup set, and a street clock. However, it can be seen in the Reddit post that the four folders have paired up in terms of similar colors in their items.

Just found out that the color of furniture in Nook Stop is not entirely random, so I made a chart from r/ac_newhorizons

Animal Crossing: Monochrome style

For the Blue and Orange Airport folders, they exhibit a more monochromatic look. The general colors of the items in both folders are black, white, and gray. The boldest colored object in the folders is the red Godzilla-like dinosaur in the Blue Airport folder. For the Green and Yellow airport folders, on the other hand, they still exhibit a monochromatic look because a majority of the colors present in the folders are still black, white, and grey. 

However, some items like the teacup sets in both Airport folders have bright, psychedelic colors as well as pastel colors. Moreover, the boldest colored object in the folders is the big bright orange vending machine in the Green Airport folder. Under the Airport folders are 26 unnamed color-coded folders that feature different furniture items in the Nook Stop shop of Animal Crossing.

The unnamed color-coded folders are divided into four major color groups: bluegreen, brown, purple, and green. First, the bluegreen section has six folders that consists of the following items: slim vending machines, cotton candy vendor carts, satellite dishes, lighthouses, and swimming pools. 

Animal Crossing: Color folders

Each folder has a different color for each common item they have. Generally, the average primary color for the folders of the bluegreen section is white.

The first folder took on a more monochromatic color scheme, the main colors being white and black. For the second folder, it exhibited more green tones in its items. As for the third folder, the colors are more diverse. The fourth folder has the most colorful items out of all the other folders. The fifth folder, on the other hand, exhibited more blue colors in its items. Finally, the sixth folder also shows diversity in the colors of its items.

Second, the brown section's folders consist of the following items: a construction sign, a lifeguard highchair, a porta potty, panoramic binoculars, and a playground item. All five folders in the brown section exhibit a diverse array of colors in the items they all have.

Third, the purple section's folders consist of only two items each: a set of two joint chairs and a telephone booth. All the folders exhibit a lot of different colors.

Lastly, the green section's folders consist of only one item each: a horse spring rider for children. Each horse spring rider has a specific set of colors.

Seems like Animal Crossing's Nook Stop isn't random after all!