If you use this plugin: https://wordpress.org/plugins/add-search-to-menu/ and want to activate the product search feature by SKU without having to use the premium one, then you can use the file I attached https://drive.google.com/file/d/1Hudj0XNFLkmuJVgSPpiUDG5ioefGmUXU/view?usp=sharing.

Extract the file and copy it to the root folder of the theme you are using.

Good luck.