How do I install Pages and Numbers to MacOS Monterey, version 12.6?

Since Apple does not keep full past version installers of these applications for direct user download, you currently would need macOS Ventura or later to get the current (v13.2) version of these applications from the Mac App Store.

If you have ever installed these applications from the Mac App Store since Fall 2013, you can use the same Apple ID to install the last compatible versions (v13.1) for Monterey. If this sentence is false, then you have no means of accessing these applications on Monterey without iCloud versions.

If true, then launch the Mac App Store, sign in with the same Apple ID as previous, and press cmd+0 (zero) to open the Purchase panel. Pages and Numbers should have indications that they can be downloaded, and there may be one or two dialogs that appear in the process. Do not click Cancel on any dialog and the pertinent one will ask if you want to install the last compatible version of these applications for Monterey.

If Apple or another reseller preinstalled Pages and Numbers at some point in the past and you did not manually install these applications, then you won't be able to use your Apple ID to reinstall them.

you can take a look at Home | LibreOffice - Free Office Suite - Based on OpenOffice - Compatible with Microsoft

it's free

Only Pages and Numbers can open their native .pages/.numbers documents, so there are no alternative applications for that purpose.

Although LibreOffice is free, it has a rather steep learning slope as it is an MS Office clone. To somewhat alleviate the learning curve, there is LibreOffice documentation in user downloadable PDFs. This documentation was actually written in LibreOffice Writer.

LibreOffice just skipped from v7.6.4 to v24.2.0 as they have just implemented a new calendar-based versioning scheme, so you want the latest release, which today is 24.2.0. It is also a good idea to read the release notes for any newly released version which are located on the download page.

LibreOffice fluff

LibreOffice Download - 2024.2.0

LibreOffice Documentation