Beginning August 13th, 2021, GitHub no longer accepts account passwords when authenticating Git operations on GitHub.com. This change was announced in December 2020:
I have now resorted to installing the GitHub Desktop App but when trying to Commit I get the attached:
Note: It accepted my Personal Access Token and managed to do one Commit since asking about this, but now I’m stuck again with not being able to commit my changes.
If you make a Google search with key “Git A lock file already exists in the repository, which blocks this operation from completing”, then you will find a lot of posts discussing about the same problem as you got. For example,