Starting today Source Tree is not accepting my usernamd and password for GitHub and keeps showing the UI to enter credentials. . Because of this issue I cannot push/pull any change. I try to update "Update Embedded Git" but that didn't solve the problem. This issue happens on Terminal as well.
The problem is that SourceTree's embedded Git client comes with git-credential-manager v1.12, which no longer works with Github since they disabled TLS 1.1 on their site. You need to get git-credential-manager v1.14. Easiest way to do that is to install a current copy of the Git client separately, and then switch SourceTree over to use that ("system git") instead of its embedded client. Alternatively, you can update git-credential-manager in your embedded client by replacing its files with the newest version from Microsoft.
(This text is here just because the site doesn't allow me to post the same message in multiple threads, even when it's the answer to all of them.)