You know you can use Ruffle if you really want Flash right?
But the only standard you need is WASM. All browsers support it. Use whatever you want to make it. In fact, Ruffle is just a WASM app.
Ruffle is not complete or comprehensive. In my test of a dozen swf ruffle could successfully display about half. Compare to the actual flash plugin Shockwave Flash 11.2 r202 (11.2.202.643) in my retro machine browser which displayed them all perfectly.
The problem is that, while there's no theoretical barrier to an authoring tool with a Director-like user experience that exports to Wasm, no one has actually written one, and it's not a small amount of work.
(I agree that we're better off without Flash, but this particular problem is real and unsolved.)