Right by default the list is filtered by the search box input with a formula like so:
SortByColumns(Filter(SharePointList, StartsWith(ComplianceAssetId, TextSearchBox1.Text)), "ComplianceAssetId", If(SortDescending1, Descending, Ascending))
In this case my "search" is only working for values stored in ComplianceAssetId, which is probably blank. So when I type the letter A my gallery is blank because none of the records start with A in the ComplianceAssetId column.
Does that make sense? If I changed the first instance of ComplianceAssetId to to a different column name that had a value that started with A then "search" would work.
Does that help?