Having a bad experience with Gemini 2.5 Pro and GameMaker Studio 2 (GML) so far

I've been reading all sorts of mindblowing experiences here and there, saying Gemini 2.5 is by far the best model for code. To help me create a game prototype and some display-related features in GameMaker Studio 2, I tried GPT-4o, o1, o3-mini, Claude Sonnet 3.5 and 3.7. It wasn't great. They kept hallucinating and making up nonexistent GML functions. Overall, it was very frustrating.

Hearing about Gemini 2.5 capabilities I was hopeful. However, it seems like it doesn't quite get GML either. It made up functions such as:

display_get_count(); window_get_current_monitor(); window_set_maximised(); 

Even pointing to what GameMaker version it was in.

var _current_monitor_index = window_get_current_monitor(); // Assumes GMS 2.3.7+ 

Checking "Grounding with Google Search" didn't help.

Maybe the problem is the relative "obscurity" of GML? But again that is a very popular game engine.

Is there any way I can make Gemini read the whole documentation or something like that? GameMaker's docs are separated in hundreds of web pages, full of images, etc., which makes just adding a link to it not work well. https://manual.gamemaker.io/monthly/en/