Many production pipelines rely on third-party extensions (e.g., XFL importers for After Effects) that broke after the 2020 update. Additionally, 2019 has a stable ActionScript 3.0 compiler that later versions changed.
Before you download, it's important to make sure your computer is ready to run the software. Here are the requirements from Adobe. Adobe Animate Cc 2019 Direct Download
Why does Adobe make this difficult?