Pages and Numbers apps for Sequoia are not available

Versions 15.4 of {Pages, Numbers, Keynote} currently in the Mac App Store require macOS Tahoe (26.*) or later.

Since the keyword reinstall is present, you can get the last compatible versions (15.3.1) of these applications for Sequoia:

1. Launch the Mac App Store and sign in with the identical Apple ID you used previously
2. Press cmd+0 (zero) to open the Purchased panel
3. Locate the applications which should have some symbology for downloading them
   1. You may have one or more dialogs with the last dialog asking if you want to install the last compatible version for macOS Sequoia. Yes.
   2. Do not click any dialog Cancel buttons

You cannot get any version of Pages v14.* from the Mac App Store unless you were on Sonoma and repeated the above steps.

If your Mac came with Pages, Numbers, and Keynote preinstalled by Apple, a third-party reseller, or someone else who gifted the Mac to you, then the outline steps I provided cannot work, and you will need to resort to using these applications from iCloud.

You cannot downgrade to Sonoma as the MacBook Pro M4 Pro shipped with Sequoia and one cannot install operating systems older than what originally shipped on the Mac.

Is the only way really to upgrade to macOS 26?

You could upgrade to macOS 27 (Golden Gate). Of course, given that macOS 27 came out so recently, upgrading to it, instead of to macOS 26 (Tahoe), might be a bit like jumping out of the frying pan, and into the fire 🔥.

You also might be able to retrieve versions of the applications that are compatible with Sequoia from your backups. That is, if you have backups …