Maybe you have the searchOnType setting set to false on your Mac.
// Search all files as you type. "search.searchOnType": true, // When #search.searchOnType# is enabled, controls the timeout in // milliseconds between a character being typed and the search // starting. Has no effect when search.searchOnType is disabled. "search.searchOnTypeDebouncePeriod": 300,

It was added as part of the 1.41 release (make sure to have at least this version):
https://code.visualstudio.com/updates/v1_41#_update-search-results-as-you-type
In full text search, results will now update as you type. This is especially helpful in scenarios like constructing complicated Regular Expression queries, where fast feedback on a query can help you to write the RegEx.
Note: This feature can be disabled by setting search.searchOnType to false, and the delay between typing and searching can be adjusted with search.searchOnTypeDebouncePeriod, which defaults to 300 ms.