I checked the repository from a non-authenticated request and it currently returns 200 OK for me:

https://github.com/w9tvx/SdrStudioRelease

So this may have been a temporary caching/session issue, a browser extension issue, or the repository visibility had not fully propagated yet when you tested.

If it happens again, I would check these in order:

1. Make sure the exact URL casing is correct. GitHub owner/repo names are usually forgiving, but copying the canonical URL from the repo page avoids mistakes.
2. Test in a private/incognito window while fully signed out.
3. Test with curl -I https://github.com/w9tvx/SdrStudioRelease or another browser/network.
4. Confirm the repository is not inside an organization with restricted visibility/policy behavior.
5. If GitHub returns 404 only for logged-out users while repo settings still show Public, collect the timestamp, URL, and a screenshot and send it to GitHub Support.

Docs:

• Setting repository visibility: https://docs.github.com/repositories/managing-your-repositorys-settings-and-features/managing-repository-settings/setting-repository-visibility
• About repositories: https://docs.github.com/repositories/creating-and-managing-repositories/about-repositories

I can access your repo in private mode. That will be cache data, remove cache and then see.