I see two possible options for you. The first one is to install the lastest python version and then symlink it so that it bypasses the outdated python version that macOS comes with. This
might help you run unsupported Calibre versions.
https://dev.to/malwarebo/how-to-set-...on-on-mac-4jjf
You can try to upgrade to the latest macOS version using OpenCore Legacy Patcher:
https://www.macworld.com/article/672...orted-mac.html