It reminds me that the show BoJack Horseman was created on Adobe Flash [1]. The creator calls himself an "Old School Flash Hack" in a same vibe like the OP.
Don't know if the latest seasons they still used Flash, maybe yes, because they just exported to video? Migrate to other tool maybe was a pain and/or changed some illustration aesthetics. Not sure if a project like that can migrate properly to Adobe Animate [2], the Flash successor.
I believe that Flash was a tool with a friendly UI/UX for casual animators but also many advanced features for pros, that's why was so popular and loved.