Closest alternative to adobe animate/flash?

We are no longer really allowed to discuss alternatives to Adobe software, but since Animate's development seems --to all intents and purposes-- discontinued or at least stuck in maintenance only limbo I see no issues providing you with a list of (free) alternatives. It's not as if Adobe is still competing in this area. 😉

For animation OpenToonz or its simplified sibling Tahoma 2D is an excellent free and open source alternative. It is actually quite a bit more feature-rich and powerful compared to Animate. More on par with ToonBoom Advanced and also including features we'd see only in ToonBoom Harmony full edition. Amazing that it is free and open source - it is a professional level animation app.

https://tahoma2d.org/

https://opentoonz.github.io/e/

A second free and open source alternative would be Blender with its 2D animation features (Grease Pencil). It provides the animator with a unique animation environment that seamlessly blends both 2d animation with 3d animation. More complex to learn, however. Also a brilliant free and professional option.

https://www.blender.org/

If you are looking for an alternative that includes both (vector) animation and programming control: nothing truly comparable exists. Animate is quite unique in this respect.  One option would be to use SVG in combination with web coding (javascript and SVG libraries). Or use Lottie files and hand-code the interactions.

If anything, Rive probably comes closest as a comparable web animation tool with interactive features. They have a basic free tier, but exporting your work will cost you a monthly fee.

https://rive.app/

A semi-free option is SVGator: https://www.svgator.com/

Do not expect the same coding features, however.