While accessing any repository in GitHub, you might get error
"fatal: unable to access 'https://github.com/repo.git/': The requested URL returned error: 403". This is because you used wrong authentication while accesing repository.
If you use usename and password while accesing repository in GitHub, then you will get error "Support for password authentication was removed on August 13, 2021. Please use a personal access token instead. remote: Please see https://github.blog/2020-12-15-token-authentication-requirements-for-git-operations/ for more information." In this linked article describes:
In July 2020, we announced our intent to require the use of token-based authentication (for example, a personal access, OAuth, or GitHub App installation token) for all authenticated Git operations. Beginning August 13, 2021, we will no longer accept account passwords when authenticating Git operations on GitHub.com.
So you have to create and use Personal Access Token(PAT) instead of password to use access Git repository. You need to create Personal access tokens(PAT) at Developer Settings option in Settings menu.
Also note that, when creating the Personal Access Token, you have checked all the required scope, otherwise you will still get 403 error.
After you have successfully created token, save it to somewhere because you couldn't get it second time. Though you can regenerate token from Setting menu, but you have to update the token at applications using this token.
So, this way, you can generate Personal access token and use it while accessing GitHub repository and others instead of password.