In 1.21.1 and before, ingredients of recipes were synced as an list of Item Stacks (with all components / nbt data) which was changed in 24w33a to only sync item types. While this functionality was never used by vanilla server, custom servers (and plugins/mods) used it to show custom ingredients (with all their components) in recipe book's ghost slots/grouped recipe preview. As ghost slot displaying (but not how it's displayed) and actual slot matching logic is running server side, there were no notable side-effects of components being present on the client (aside of visuals that is). With this functionality no longer being present, recipe book loses it's usability on servers that add a lot of custom content with custom recipes.