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/
I have been able to search logged out within a repository, up to this year. I think what you are referring to is search across all repositories. That was indeed disables a while ago. But things did change this year, unfortunately. So yes there is a legitimate and new issue… Once more.