1.Is it possible to display a default country (France), and not the whole world?
Yes, see this doc for how to set up a map that shows listings from one location: https://wpgeodirectory.com/docs-v2/integrations/maps/#location
2. How to display 100 results by default? (and not 10)
For the archive and search pages, you can adjust the “Post per page” setting in WP – Settings – Reading – Post per page
For the location page you will change the values of GD Listings to show more listings.
3. Why do I have some cities and regions posted? (cf. picture)
That will show 10 recent locations from the site database.
4. Why do I only have one result when I search for the city of Paris? And the message “No Records Found. Sorry, no records were found. Please adjust your search criteria and try again.”
I see 14 results, but only one per page. One per page is either the posts per page setting or a theme setting that sets posts per page, probably the theme, but I cannot login so I cannot check that.
5. How can I manage the meta title & description of
The Titles and Metas settings are what you want: https://wpgeodirectory.com/docs-v2/geodirectory/settings/general/#titles-and-meta
Please update WP Admin credentials if we need to check the settings.