No matching distribution found for numpy==1.19.3

This error message indicates that the version of numpy you are trying to install (1.19.3) could not be found in the repositories that your package manager is searching.

There are a few possible reasons for this. One possibility is that the version you are trying to install is no longer supported or has been removed from the repositories. Another possibility is that there is an issue with the repositories themselves, such as a connection problem or a misconfiguration.

To resolve this issue, you could try installing a different version of numpy that is available in the repositories. Alternatively, you could try updating your package manager and/or refreshing your repositories to see if the desired version of numpy becomes available. If neither of these solutions work, you may need to seek assistance from the maintainers of your package manager or the numpy project.