Pages frozen and haven't saved my work, how can I recover this file?

Leave Pages hung as it is. Click on the Desktop to make Finder the current application. Press shift+cmd+G to open the Go to Folder dialog. Copy and paste the following in that window:

~/Library/Containers/com.apple.iWork.pages/Data/Library/Autosave Information

and then press return. A new Finder window will open on that location. You should see an Unsaved Pages Document present. Drag and drop that to your Desktop. Close the current Finder window.

Press option+cmd+Esc to select and force quit Pages. You will lose the unsaved content opened in Pages. Press and hold the shift key when you relaunch Pages as that will prevent it from reloading its last saved execution state.

On the Pages File menu, choose Open… and select the Unsaved Pages Document on your Desktop. Provided it still contains content, press File menu > Save… and after giving it a proper document name on your Desktop, save it. That will enable Pages Autosave for this document so future content will not be lost.

Tested: Pages v14.3, Sequoia v15.3.2.

Pages will only enable autosave of your changes after you manually save the document once. I always recommend doing that after selecting the template and before one enters any content. Even Microsoft Word will not perform autosave unless you select that in its Preferences > Save Panel.

Considering the first paragraph, I also recommend that one employ Apple's built-in Time Machine for hourly backups — though this will not back up unsaved documents. Your content loss is an information issue, not a limitation of macOS.

A measure of knowledge about how autosave works, indeed, even a question here before you began using Pages could have saved you considerable disappointment. Not every Apple application on your Mac provides autosave and even more rare are non-Apple applications.

I am aware of Google Docs and still do not use them. I don't care to share everything I write with Google's archiving processes.