More details. Google will remove the Search Console rich results report for Sitelinks Search box and Google will also stop highlighting the markup in the Google Rich Results Test.
Google said you can remove sitelinks search box structured data from your site but added “:there’s no need to do so.” “Unsupported structured data like this won’t cause issues in Search, and won’t trigger errors in Search Console reports. If you decide to remove sitelinks search box structured data, note that site names also uses a variation of WebSite structured data, which continues to be supported,” Google added.
Why we care. The Sitelinks Search Box can be a quick way for searchers to do quick internal search searches for your website directly from the Google search results page. Google said it was not used as much as it used to, but if you did get a lot of usage out of this feature, then you may be impacted in some way.
Maybe consider making your internal search box more prominent if you are concerned that Google won’t provide this for your users directly in Google Search.