Hi there,
the only thing you can do is to limit the width of the container.
Most of your sites content is limited to the 1800px Container width.
However your first section breaks out of that because that Elementor section is set to Stretch Section. This uses Javascript to force it to fill the screen regardless of what container width you impose.
The only solution, to the best of my knowledge, is NOT to use the Stretch Section option.
Increase the Container Width to accommodate the maximum full width section you want.
For those non full width sections you can set their content width in Elementor.
The Layout Element allows you to change content width for individual pages:
https://docs.generatepress.com/article/layout-element-overview/