The root cause of this issue is that the iOS keychain imported only the client public and private keys, but not the CA certificate. A PKCS#12 file (.p12 or .pfx) is a file format that contains a certificate and its private key, optionally protected by a password. A PKCS#12 file can also contain intermediate certificates or root certificates that are needed to verify the certificate chain. However, when importing a PKCS#12 file into the iOS keychain, only the certificate and its private key are imported, not the CA certificate. This means that the iOS device cannot verify the authenticity of the certificate, and displays the error message "mbedTLS: ca certificate undefined". To fix this issue, the CA certificate needs to be imported separately into the iOS keychain, either manually or using a configuration profile. Verified Reference:
https://developer.apple.com/documentation/devicemanagement/certificatepkcs12
https://support.apple.com/guide/deployment/distribute-certificates-depcdc9a6a3f/web
https://openvpn.net/faq/how-do-i-use-a-client-certificate-and-private-key-from-the-ios-keychain/

Step by Step
Database activity monitoring (DAM) tracks user actions within databases and generates alerts for anomalous behavior, such as unauthorized access to sensitive content.
Database field tokenization protects sensitive data but does not monitor access.
Database decoy involves creating fake data to detect misuse but is unrelated to monitoring.
Database integrity enforcement ensures data accuracy but does not generate access alerts.

Executing the files in the sandbox on the web proxy is the best solution to reduce the risk of employees downloading and opening malicious files from the internet. A sandbox is a secure and isolated environment that can run untrusted or potentially harmful code without affecting the rest of the system. By executing the files in the sandbox, the web proxy can analyze their behavior and detect any malicious activity before allowing them to reach the corporate workstations.

OAuth, which stands for Open Authorization, is a standard for authorization that enables secure token-based access. It allows users to grant a web application access to their information on another web application without giving them the credentials for their account. OAuth is particularly useful for rapid authentication, flexible authorization, ease of deployment, and offers high functionality at a low cost, making it an ideal choice for new web-based applications. This approach is well-suited for situations where web applications need to interact with each other on behalf of the user, without sharing user's password, such as integrating a geolocation application with Facebook. OAuth uses tokens issued by an authorization server, providing restricted access to a user's data, which aligns with the objectives of rapid authentication, flexible authorization, ease of deployment, and cost-effectiveness​​.

Isolating the servers is the best immediate action to take after reporting the incident to the management team, as it can limit the damage and contain the ransomware infection. Paying the ransom is not advisable, as it does not guarantee the recovery of the data and may encourage further attacks. Notifying law enforcement is a possible step, but not the next one after reporting. Requesting that the affected servers be restored immediately may not be feasible or effective, as it depends on the availability and integrity of backups, and it does not address the root cause of the attack. Verified Reference: https://www.comptia.org/blog/what-is-ransomware-and-how-to-protect-yourself https://www.comptia.org/certifications/comptia-advanced-security-practitioner