How can i identify all FILTERS that are shared with PUBLIC?

You can pull this from the REST API without any app. Call:

https://your-domain.atlassian.net/rest/api/3/filter/search?expand=sharePermissions

Page through the results and look at each filter's sharePermissions. A type of global means it is shared with any logged-in user (org-wide), and loggedin / anonymous-style permissions are the ones to watch. Anything with those is effectively exposed beyond a single project. You can do the same for dashboards via /rest/api/3/dashboard/search?expand=sharePermissions.

The tedious part is that the API paginates, mixes owners and permission types, and gives you raw JSON, so turning it into a clean "here is everything that is over-shared" list takes some scripting, and you have to re-run it periodically.

I built a small read-only app that does exactly this, Filter Exposure Guard. It lists every filter and dashboard with its exposure level (public, org-wide, shared, private), owner, and risk signals in one view, so you can spot and fix the over-shared ones. Sharing in case a ready-made tool is easier than the script.