where to find updates for Pages?

The last version of Pages for macOS Mojave is v10.1. Apple frequently ties specific versions of Pages to minimum operating system versions and right now, the current Pages v12 requires macOS Big Sur (11.*) or later.

If you don't have Pages v10.1 on Mojave, ensure that what you have is backed up, and then move it to the Trash and empty the Trash. Next, launch the Mac App Store and sign in with the same Apple ID that you used to install Pages previously. Press cmd+0 (zero) to open the Purchases panel, and with Pages, click its Update button.

A first dialog will appear informing that you need to upgrade the operatings sytem to get the current Pages. Do not select Cancel, and just acknowledge that dialog. A second dialog should follow offering to install the last compatible version of Pages for macOS Mojave. Choose that and you should have Pages v10.1 installed.

The App store will offer the latest update of Pages for your version of macOS, which I think is Pages version 10.1 for Mojave.