Where is the link to Monterey 12.6.3

In Software Update, and based on the fact your are running macOS 12.6, you should see the main upgrade for Ventura 13.2.1, and well below it, the text Another update is available with a More Info… link. If you have that and click on that link, a new update panel will appear with macOS 12.6.3 for installation. Ventura will not be installed.

Apple - Support - Downloads

carries all stand alone installers prior to 10.15.6

Keep in mind combo updates are to update any version of the upgrade prior to the combo update.

I.e. 10.15.6 combo will update 10.15, 10.15.1, 10.15.2, 10.15.3, 10.15.4, 10.15.5 to 10.15.6

10.15.6 delta will only update 10.15.5 to 10.15.6.

Not direct link for the 12.6.3 update as Apple Discontinued offering Standalone Update after macOS 10.15 Catalina

The user can Manually download the latest Full Version of Monterey which is version 12.6.3

Notation - the Full Version 12.6.3 is about 12.xx GB in size

Run the Terminal command below

softwareupdate --list-full-installers

This will Only Search for Full Versions of macOS this computer Qualifies to Run

To actually download the 12.6.3

Following command

softwareupdate --fetch-full-installer --full-installer-version 12.6.3

The will download the 12.xx GB Full Version of 12.6.3

It places a New Application in the applications Folder of this computer

It Does Not Auto Launch

When ready, launch the application like any other apparition and follow the prompts and instructions.

Go to System Preferences->Software Update.

You are welcome.