Fixing the Advancements Window Not Going Fullscreen

First Checks

If the window still opens at the vanilla size, work through these in order:

1. Confirm the mod appears in your mod list for the profile you actually launched. It is common to install it into one instance and launch another.

2. Check that you are not running a different advancements-related mod at the same time. Two mods editing the same screen usually means one silently wins.

3. Restart the game completely rather than reloading a world, since screen changes are applied at startup.

Conflicts and Compatibility

This is a client-side mod, so it does not need to be installed on the server, and it will not break anything for other players. That also means server-side plugins cannot cause it to fail.

The usual culprit is another client mod that resizes or replaces the advancements screen, or a general UI overhaul mod. Temporarily disable other interface mods one at a time to identify the conflict. If the window is fullscreen but the layout is cramped or overlapping, that is a sign of a rendering conflict rather than a missing mod, and the same disable-one-at-a-time approach applies.