SharePoint Hub Site can't link to another hub site?

Dear All,

Currently I have a main landing page to add all the division\department links under Quick link.

This main landing page has been promoted to hub site.

However I have another concern that HR main site which is promoted to hub site also. The reason is other HR sites (Site collection) will be associated to HR main site (Site collection) due to microsoft direction (No subsite creation). 

I would like to have cross site search to HR main site also from landing page. 

What shall I do to achieve this requirement?

Please advice.

Thanks.