I would start with OpenToonz: https://opentoonz.github.io/e/index.html https://opentoonz.github.io/e/index.html It’s used by Studio Ghibli for making Anime and

I would start with OpenToonz: https://opentoonz.github.io/e/index.html https://opentoonz.github.io/e/index.html It’s used by Studio Ghibli for making Anime and I know for sure that it supports tweening. And it’s free and open source.