I have the Scratch 3.29.1 offline editor and the search option in sounds isn't working.
My browser / operating system: Windows NT 10.0, Chrome 146.0.0.0, Adobe Flash 10

I think the Scratch offline editor has had random issues with sounds before, for editing or large audio files: https://scratch.mit.edu/discuss/topic/367559/?page=1#post-3676877

it's not updated as often as the website, some features like search in your case, can stop working. Maybe try the online Scratch editor instead.

What search option are you talking about?

the online editor is so broken too