When exactly will Monterey 12.7.6 stop security updates?

Microsoft only supports current releases of Microsoft 365 or Office 2021/2024 for new Mac installations on Ventura, Sonoma, or Sequoia. All Microsoft updates have ceased for their applications on Monterey or earlier operating systems.

At Apple's discretion, they may issue a critical security update for Monterey, but otherwise, Apple support of Monterey has ended.

Your Early 2015 MacBook Pro cannot upgrade beyond Monterey and at 10 years old, it is time to consider a newer replacement should you want to stay current with supported versions of macOS or Microsoft applications.

Or, you could consider continuing to use your MBP with Monterey and choosing instead to use the free LibreOffice Suite for Microsoft document compatibility, or even the lower cost (than Microsoft) SoftMaker Office 2024/NX suite which is also visually and document compatible with your existing Microsoft applications. Neither of these two solutions will end support any time soon for Monterey.

macOS 12.7.6 was likely the last update for Monterey. It was released July 29, 2024 along with updates to Ventura and Sonoma. Since Sequoia was released there have been updates to Ventura, Sonoma and Sequoia but not to Monterey. See: Apple security releases - Apple Support

Updates for the last 3 releases is the usual pattern.

Microsoft also provides updates for their software that is running on the 3 most recent macOS versions.

An early 2015 MacBook Pro cannot be upgraded beyond Monterey.

The current version of Safari is 18.3; the latest version of Safari that will run on Monterey is Safari 17.6.

For security reasons you may want to use a 3rd party internet browser that supports running their current version on your Mac rather than Safari. One option is Chrome: https://www.google.com/chrome/

There is also a user tip about which browsers will work with each operating system: Browsers by Mac operating system - Apple Community

Apple implements better security in the operating system to thwart attackware than Microsoft Windows 11 or even current Linux distros.

Apple Platform Security - Apple Support

A newer Mac that can still get current Safari updates would need to support Ventura or later. I use Safari, since that is where years of my bookmarks are saved, and use The Brave browser for better privacy and security than Firefox or Chrome can provide.

I am using Office 2021 for Mac Home and Business on my M4 Mac Mini Pro and have Office 2021 Professional Plus installed in my Windows 11 Pro guest supported by Parallels Desktop Pro on my 2020 iMac. Both Macs are running Sequoia.

1. My MS Office has stopped getting updates but does not bother me as all works fine. Not really concerned about Office updates the way I use the program. If the reminder yellow bar is annoying it can be stopped by removing the update file in MS office library. Go to library/application support/MS and look for the Mau or the MAU2.0 and find the msautoupdate.app file and move to trash

Chrome is the most widely used browser according to https://en.wikipedia.org/wiki/Usage_share_of_web_browsers

I mainly use Safari and only use Chrome when I'm having a problem with a site using Safari. Safari has a few features I like (e.g., fingerprint sign in to Apple sites like this forum).There are quite a few strongly negative opinions of Chrome, many of which are related to their collection of data for advertising. Personally, I have no issues with their advertising data collection but many strongly object.