I gave Marina a pink cute fishing pole and she displays it in her house sometimes but then I also see her walking around with it and using it to fish instead of the normal one.
One of the villagers gave Marshal an umbrella. Now he displays it in his house. It's not exactly an issue, but he uses it on rainy days. I guess he originally owned a mint umbrella. But it was never on display in his house and I'm afraid to give him a mint umbrella.
A few of my villagers have interacted with a drinking fountain and popcorn machine when they walk by. I've seen Gruff and Rocco play the recycled can piano I made but it's pretty rare. Sterling also interacts with sports equipment such as a volleyball for example.
Not exactly a ‘using an item’ but my husband has a fish stand set up and the villagers (especially the nature hobby ones, (specifically I saw zucker do this) was looking at the fish in containers while referring to a fish reference book (like some of them do with the flower reference books). It’s not a direct interaction but I thought it was pretty cute, and I liked that they had the ability to ‘recognize’ the fish and were interested in them.
I have a Spinning Wheel near Able's and Merengue always like to play with it. I also put a Bamboo Drum near the entrance and it's cute seeing one of my villagers interacting with them. The zodiac items like Aries Rocking Chair, Virgo Harp and Libra Scale are interactable as well.
If you go onto Nookplaza, and click the 'Interactable' filter, you can see the list of items that animals will be able to interact with.
A tip I keep in mind when decorating my island is that if you are doing a side-step to get into an area, then your villagers will not be able to access it. Same with areas that have stepping stones. So you will want to make sure there is enough space around so they can move freely.
Oh, another thing I've seen are interactions with items that players can't even do! I put one of those potted plants (like a cypress or monstera or whatever) outside by Plucky's house, and I've seen her stop whole walking past it, pull out a little spray bottle, and water it!