You can TAS Flash 9 games in libTAS through gnash-sdl. Instruction linked at the top of this post
You can also run standalone Adobe FlashPlayer in libTAS, but its support is incomplete. There's also work on supporting Ruffle
If you're crazy, you can also run Adobe FlashPlayer inside PCem inside libTAS (inside Linux or WSL). Setup is described in Post #471467
We already have submission support for Flash inside libTAS, but nobody made an optimized movie (that would also sync for judges and publishers) of it yet.