How can I install MacOs Ventura (13.x) on my MacBook Air (11 early 2015)

Microsoft has a policy of only supporting the three most recent versions of macOS.

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

"If you continue with an older version of macOS, your Office apps will still work, but you'll no longer receive any updates including security updates."

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

There is LibreOffice . I believe that it will run on Catalina or later (including Monterey).

You can’t. That machine can not run anything later than macOS 12 Monterey.

Your Mac can only be updated up to the latest version of macOS 12 Monterey.