Edit:
Since theres been some confusion with dates
In 2016 github made site side searching login only and hid the search bar if you werent logged in. This didnt include searching within a repository so that could still be done, just not all repositories
This year was the change being referred to in this link which made repository level searching require logging in
Blog post: https://github.blog/changelog/2023-06-07-code-search-now-requires-login/
GitHub search simply won’t find search terms that I know are there (because I can grep them in my local repo). It also fails to search all branches. There’s also insufficient filtering for filetypes or paths.
Maybe I’m just spoiled from having used OpenGrok, as well as knowing how to use basic tools like find and grep, all of which I find substantially more useful.