Thanks for expressing your issue in detail. Actually, our theme is fully compatible with the Elementor plugin and its feature “flexbox Container” as well. All of our theme widgets are compatible with it also. It is totally up to you whether you want to use “Flexbox-Containers or Old sections” The choice will be totally yours.
Regarding setting the container full width please refer to these articles: https://elementor.com/help/set-flexbox-container-size-behavior/ and https://elementor.com/help/full-width-not-working/
I hope your issue will be resolved.