creating a structure

I am creating the gtm_data struct in the main controller with $gtm_data = new stdClass();
How can I just declare gtm_data as a Global so every module has access to it?

$gtm_data is not a struct, because PHP does not have structs.
$gtm_data is an object.

And it is recommended not to use global variables.
Why don't you pass $gtm_data to the model?

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