I've also suffered this issue. I created a support request and the conclusion was that my windows 10 version was too new so that's why search project functionality was not working properly. Basically Siemens has not yet tested most of its software under the newest version of windows 10.

You can access https://support.industry.siemens.com/kompatool/ and download an excel file with windows 10 compatibility under Download of operating system compatibilities. You can check your windows version typing winver in the windows search box. Probably you will have the newest version like mine, 21H1.

I confirmed that I’m using 20H2.

20H2 is on the Compatibility list for WinCC Unified Engineering (TIA Portal) V17.0.

Do you know any other cause?

With V17 upd1  , I can search into script text.

https://support.industry.siemens.com/cs/us/en/view/109784441

Yes! It's also working for me now, but I would say it was after V17 Upd2. I think it wasn't working for me with V17 Upd1, but I cannot really confirm.

Anyway, it's good news for our daily producitivity.