My browser / operating system: Windows NT 10.0, Chrome 139.0.0.0, Flash 32.0 (release 0)
Dont know if its a exstenssion doing it but whenever I try to import sound it than it asks for picture file types and I have to select the all files option and after selecting a .mp3 or .wav it says its importing but never actually does

Have you tried turning off any extensions? It works fine for me.
My browser / operating system: Windows NT 10.0, Firefox 142.0, No Flash version detected

Wasn't happening to me (I think I saw someone else reporting this)
My browser / operating system: Windows 7, Chrome 139.0.0.0, No Flash versions detected
Edit:
https://scratch.mit.edu/discuss/post/8675527/
The topic creator was on Windows 11
Edit 2:
Also, it showed sound file extensions for me
Edit 3: By the way, what version of Windows are you on (Chrome now seems to report Windows NT 10.0 for all Windows versions without modifying your user agent, and Windows 11/10 both are NT 10.0 as well)

My browser / operating system: MacOS Macintosh X 10.12.6, Firefox 142.0, No Flash versions detected
Can't replicate still