You can't do that anymore. It was possible a while through options, but now they removed that to force everyone to the new "experience".

I think the main thing that we can do is keep reporting and upvoting issues with this.

Please feel free to upvote:

Deprioritize "smart" abbreviations in Code Search

https://developercommunity.visualstudio.com/t/Deprioritize-smart-abbreviations-in-Co/10694279?sort=newest

(might be most related to yours)

Lots of irrelevant files in Code Search cluttering search results

https://developercommunity.visualstudio.com/t/Lots-of-irrelevant-files-in-Code-Search/10887579?sort=newest

Visual Pass on the new Code Search

https://developercommunity.visualstudio.com/t/Visual-pass-on-the-new-Code-Search/10525569?sort=newest