I noticed that, for some sites, if I look for i.e.: "benny ben", I don't see Sitelinks, instead if I look for "bennyben" (which matches with the domain name) then I see them. How can I make Google showing Sitelinks for both searches?
Sitelinks normally are those pages that have more traffic than other pages of that particular website and have better structure. Keep your most hot content for which you want to rank and appear as Site Link, put them in menu bar for example, if you want sitelink of a page focusing on iPhone XS, put link of iPhone XS category (or post/article) in start of navigation menu. This will put it at first of site links in Google.