Late 2015 iMAC OS upgrade with microsoft 365

If you want to upgrade macOS to Mojave, Catalina, or Monterey, see

How to download and install macOS - Apple Support

If you upgrade to Catalina or Monterey,

• 32-bit applications will break
• iTunes will go away, replaced by separate applications (Music, TV, Podcasts, Books) and the Finder
• You will be able to run current versions of Firefox, LibreOffice, and the commercial Affinity V2 applications, but
• You will not be able to run current applications from the likes of Adobe and Microsoft

Quick addendum because I found the right Microsoft page: https://support.microsoft.com/en-us/office/upgrade-macos-to-continue-receiving-microsoft-365-and-office-for-mac-updates-16b8414f-08ec-4b24-8c91-10a918f649f8...

Starting with the September 2024 update (16.89) macOS Ventura or later is required to receive updates.

The August 2024 update (16.88) is the last build to support macOS Monterey. 

The September 2023 update (16.77) is the last build to support macOS Big Sur. 

The October 2022 update (16.66) is the last build to support macOS Catalina.

I believe that current versions of LibreOffice will run on Catalina and later. If you dig in the LibreOffice archive of unsupported old versions, you may even find one that runs on High Sierra. (The archive is not well-organized in regards to helping you find the latest version of LibreOffice that is compatible with a particular version of macOS, but there is nothing to deliberately lock you out from running an unsupported version on an old Mac.)

My recollection (which may be mistaken) is that

• Version 7.4.7 was initially compatible with High Sierra
• I installed it on an old iMac that was running High Sierra
• Some time after that, they revised 7.4.7 so that it required Mojave

Thus, if you're looking for a copy that works with High Sierra, you might try looking just a little before 7.4.7.

kieta257 wrote:

I tried to upgrade to my Micrsosoft 365 so that I can upgrade the OS, but it states it needs OS12 or later which is newer than Monterey.

Microsoft Support – Upgrade macOS to continue receiving Microsoft 365 and Office for Mac updates

"Note that new installs of Microsoft 365 for Mac require macOS Ventura or later."

It is as far as Microsoft is concerned. They only support the three latest versions of macOS.

Here is the release history for Office for Mac: https://learn.microsoft.com/en-us/officeupdates/update-history-office-for-mac

Monterey is required for version 16.78 or later: https://officecdn.microsoft.com/pr/C1297A47-86C4-4C1F-97FA-950631F94777/MacAutoupdate/Microsoft_365_and_Office_16.78.23102801_Installer.pkg (this is the version without Teams).

Since Microsoft only supports the current and previous two versions of macOS, Ventura may be required for 16.90 or later - not precisely sure where the cut off line is drawn since MS releases and macOS releases don't precisely line up.