Updates

Had to make a masked run on the grocery store…

Reboot your Mac into Safe Boot mode by depressing the shift key until the boot progress bar appears. There is a bunch of house-keeping tasks ongoing, so it will be slower than normal, and their may be screen aberrations too. All normal.

While in Safe Boot mode, see if you can open the Mac App Store, and try again to install these applications. Reboot normally, and try again in the Mac App Store, if it did not work in Safe Boot mode.

All of this should not be necessary, but sometimes, things need a push to get them resolved.

Open the Mac App Store. Click on your Avatar/Name in the lower left corner. This will take you to what was previously the purchased tab in earlier version of the Mac App Store. If you see Pages, Numbers, and Keynote present, their should be an Update button, or symbolic download arrow. Click that to download the respective version 10 of each application.

If you do not have these three applications in the first paragraph, then use the Mac App Store search field for ____ app, to open the respective ___ app page. Click the Download button for each application.

In the Finder Window Favorites Sidebar, click on Applications, and then locate Pages. Press ⌘+i to open the Get Info panel. What version does Pages show in that panel? If it is 10.0 then you already have the updates.

Are you using a different Mac than shown in your Profile, and not running Mojave 10.14 or Catalina 10.15?

The downloads should still work with Catalina 10.15.4. I had to go to the Mac App Store myself to get them, as they weren't showing up in Catalina as updates in the Mac App Store.

Click once on the Macintosh HD icon on your Desktop. Click ⌘+i to Get Info on it. How many GB appear in Available? Also, are you signed into the Mac App Store with the same Apple ID as was associated with the macOS installation?