There are two areas to search within Splice INSTRUMENT, each with their own functionality.
Top Bar:
The search bar at the top of the plugin will search all available content from the Discover tab, searching by preset name, pack name, and pack category. Clicking this search bar will take you straight to the Discover tab, which allows you to quickly install the sound that you find after searching.
You can choose if you want to search by Packs, Presets, or All.
From this page you can also filter by tags, which work in combination with your search input.
Library:
The search bar found within the "Library" tab will search only your currently installed content, and will search based on your selection of Presets or Packs in the lower tab.
For more information on the Library search, see the article here: Where do I find `My Library`?