Every time I see SVG mentioned with Flash I just think it's immensely ignorant. No offense, but programmers love to think of "vectors" as SVG because it's all they know. For several years I kept hearing people say "we have HTML5 and SVG now, so we don't need Flash anymore." And with that Flash animations and games were lost forever and I'm still bitter about it.

For artists, SVG is probably the worst vector format imaginable. In fact, I'd say any project that uses SVG as backend is doomed to fail with artists. It's pretty much a red flag at this point that if "supports vector" means "support SVG" they're doing it wrong and just chose the easiest to implement vector graphics because you probably have a billion open source SVG libraries at this point instead of rolling their own proprietary vector rendering algorithm that actually improves the artists' workflow.

To answer your question, the important thing about Flash wasn't the vector rendering but the vector art authoring tools. You could make Inkscape work like Flash, but nobody has done that yet. All you need is a brush tool that automatically does union of shapes of same color and subtraction of shapes of different color so the whole layer is always "flattened" with no shapes overlapping. This is the sort of thing that made Flash exceedingly easy to use for artists. It was a vector art program that worked exactly the same way as a raster digital art program. It thought of vectors not as shapes that the program was going to render but as paint strokes on a canvas.

If you were building a vector art software today you probably would want all sorts of things that SVG doesn't provide, e.g. line art with varying thickness based on tablet pressure (although Flash didn't need this, since you could draw shapes instead of strokes). You might also want to take a look at OpenToonz' vector implementation, which has "fills" that automatically expand when you change the enclosing strokes and an indexed color palette system, and CSP's line art vectors that let you use textured raster brushes with settings like dab scattering in vector strokes.

By the way, I also believe the idea that HTML5 could replace Flash games was insanely stupid. Anyone could make a Flash game and deploy it to web browsers in one click. Do that in HTML? With Javascript? Which means you need to download all these images/audio from the Internet? You want to play it locally? CORS issues, baby! Now you need to turn this mess into an electron app or use the most disgusting build step imaginable to turn whole jpegs into a base64 strings so you can create a single HTML file that is several megabytes. How did the entire world convince themselves that this was an actual replacement of Flash's functionality is honestly beyond me. For Flash websites, sure, you have <video> now, but for everything else that Flash provided there has never been a proper replacement (at least until Godot/Unity started WASM'ing, but that was a long time after).