Adobe ended support for Flash Player in 2020 — HARMAN now jumped in to support Flash until 2023... but I don't believe that is has a great future.
TexturePacker's Flash Unpacker is an add-on for TexturePacker to extract animations sequences as sprites and pack them into a sprite sheet. We've introduced that feature in 2011 with TexturePacker 2.4.0.
It currently looks like not many users are still using that feature. On the other hand for us it's additional work since we have to test it with every TexturePacker release on 2 platforms. We have plans to remove that feature from TexturePacker with one of the next update.
If you really need the .swf support contact us at supportXXXX@codeandweb.comand we might keep it for some more time.