The Godot game engine has some really powerful 2d animation tools. It's completely free and open source, and its original creators used it for 2d point-and-click adventure games with lots of animation.
Here is some documentation on its animation features:
You would have to make your animations as a "game" and then record video/take screenshots, though, so it might be overkill.
+10000000000 for blender if you like well designed things but whatever makes you comfortable really
https://hexbear.net/post/84366/comment/914972
Blender is really the best as the 3D workflow let's you do perspective naturally instead of with scaling. You can convert vectors into grease pencil objects and rig them with bones too so you can puppet your drawing without having to re-draw every frame.
I used synfig recently and found its workflow pretty rough. Definitely play around with trying different stuff in it before you get too far with your project.
