I get that Flash hit a sweet spot. I'm not sure I get why nothing has really replaced it. There are other apps that give you animated vector graphics, in an IDE, with coding.
Here's 2?
https://cavalry.scenegroup.co/
I believe Unity doesn't do flash style vector animations. It will take in SVGs, turn them into meshes and apply skeletons. That said, it has replaced Flash in turns of the 1000s and 1000s of web games made with it.
https://itch.io/games/platform-web (majorty are Unity?)
Fun history: There was a flash like (vector animation program) for the Apple II called Fantavision.
https://youtu.be/8_Bm8bidrpE?t=40
It would export executables IIRC.