If you want to own the files permanently (offline viewing), here are the best platforms where you can legally.
Furthermore, with the rise of , many older movies (1997-2005) are being "remastered" by fans to 4K. If you see "4K AI Upscaled" in a download search, ensure the source file is at least 10GB to be legitimate. Detective Conan Download Movies
Search using both English and Japanese titles: If you want to own the files permanently