Security Agent causing high cpu

I do not see such a process on my system. I found a reference in one of the Developers manuals:

Security Agent

The Security Agent is a separate process that provides the user interface for the Security Server in macOS (not iOS). Its primary purpose is to request authentication whenever an app requests additional privileges.

When the Security Server requires the user to authenticate, the Security Agent displays a dialog requesting a user name and password. The advantages of performing this action in a separate process are twofold. First, an application can obtain authorization without ever having access to the user’s credentials (username and password, for example). Second, it enables Apple to add new forms of authentication without requiring every application to understand them.

The Security Agent requires that the user be physically present in order to be authenticated. Because the graphical user interface elements can’t be used through a command-line interface such as the Terminal app or a secure shell (ssh) remote session, this restriction makes it much more difficult for a malicious user to breach an app’s security.

Perhaps this may help you track down what is causing the problem. One thing you might try:

About Safe Mode

• Use safe mode to isolate issues with your Mac - Apple Support
• Playing Safe- what does Safe mode do?

Boot into safe mode then restart normally. This clears out a number of caches which may stop the process from eating up so much CPU time. Safe mode is much slower than a normal startup, so be patient.