I had that problem what worked for me is to send your sim to the lot switch it to generic put the fish in and than back to Art Center or Museum. Not sure if it bugged on my end that’s why it worked or it just works lol. Let me know if that helps. If you save it to the library for other saves they will disappear ? but your collectibles, plants, and art should stay. Check mine out the front lacks luster but I am happy with my rainforest that has a small rock fountain and my aquarium exhibit
https://www.ea.com/en-gb/games/the-sims/the-sims-4/pc/gallery/CAB10DC8882B11EA8677335C231BF121?category=all&searchtype=hashtag&sortby=newest&time=all&searchquery=%23sandbox&max=50&maxis=false
