The left panel, Filter preferences, contains:

• General > Only Selected - show only meals already on this date's menu (not shown on Preset Menu pages).
• Portions - the default portion (named after your Portion Size Default Name setting) and every portion size; ticking one shows only meals that offer that portion. On the Catering Menu the list contains catering portion sizes.
• One block per meal category group (for example Type, Diet, Protein) listing its categories; tick any to filter.

Above the results, the Search box matches the meal ID, name, internal name and description as you type (with a short delay). Results load 10 at a time - press Load More for more. On small screens the filter panel collapses behind the funnel icon.