Making the Structures Backgrounds Show Up on Your Loading Screens
If you installed the pack but the loading screen still looks plain, the problem is usually one of three things: the pack is not selected, another pack is overriding it, or the mod is not generating a loading screen for that transition.
Check Pack Order
Open Options > Resource Packs. The Structures pack must be in the selected (right) column. If you run several packs, the one lower in the list wins for any file both packs touch. Move the Structures pack so it is not being overwritten by another background or UI pack.
Check the Mod Side
Loading Backgrounds only draws images during actual loading transitions, such as joining a world or changing dimensions. Quick reloads or already-loaded chunks may skip the screen entirely. Try quitting to the title screen and loading a world again to force a fresh loading screen.
Check for Conflicts
Some packs bundle their own loading images. If two packs both provide the same background files, only one set will appear. Temporarily disable other resource packs to isolate the Structures pack, confirm it displays, then re-enable the rest one at a time to find the culprit.