The certificate is fine. It is an auto renewed LetsEncrypt certificate
Code:
wget -nv -O/dev/null https://download.calibre-ebook.com/linux-installer.sh *
2024-12-10 05:10:08 URL:https://download.calibre-ebook.com/linux-installer.sh [35050/35050] -> "/dev/null" [1]
And ssl certificate test report
https://www.ssllabs.com/ssltest/anal...ibre-ebook.com
Probably your system is missing some CA certificates.