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/
searching across all of github was made to be logged in then
repository level searching though is relatively recent. Heres the blog post about the change dated in June this year https://github.blog/changelog/2023-06-07-code-search-now-requires-login/
This comment by an employee in the thread also calls out it was in 2023 and links to the blog post
Half year too late for that outrage anyway :)