After upgrading it happens that cups is unable to print and reports:
Unable to open print file: Permission denied
It has something to do wit the cups configuration.
Therefor delete the /etc/cups directory content or move it to a backup directory at /root/cups-backup just in case.
Finaly reinstall some packages so the configuration files are recreated.
apt install --reinstall cups-daemon printer-driver-cups-pdf
Maybe a restart of some daemons is needed like.
systemctl restart cups cups-browsed
cups-pki-invalid)To solve this delete the SSL certificate in /etc/cups/ssl for the printer or all of them.