They recently added some new features. If you setup a parameter as a scene variable (last in the list of parameter types) You can then set another variable to the that variable using copy variable to function parameter under [other] conditions [Event functions]
This only works with scene variables but it seems to work with all variable types like arrays and structures. There’s also an action to do the reverse.
For a global variable, I think you would need to use JavaScript.
The name of the actions are a bit cryptic.
https://wiki.gdevelop.io/gdevelop5/all-features/advanced/reference/