Site Health Status?

Hi. It shows me “1 recommended improvement”:

Have a default theme available
Security
Themes add your site’s look and feel. It’s important to keep them up to date, to stay consistent with your brand and keep your site secure.

Your site has 1 installed theme, and it is up to date.

Your site does not have any default theme. Default themes are used by WordPress automatically if anything is wrong with your chosen theme.

BUT when I open it – I see no way to “improve” anything?…

The page I need help with: [log in to see the link]