With the release of Simple Model Editor 6.7.1 (part of Installer 2021.06), a new function to count the entries on the page became available. To use the function, you need to tick the checkbox field here: Overview Model Editor/Overview/Amount of Entries/Show Amount of Entries.
To make the number visible, you need to add a label first (Overview Model Editor/Model settings/Labels).
Example of use in PI :
