You can select which Theme Elements you don’t want to be displayed, title, sidebards etc and set the Page Builder container to full width. Then use the display rules to set which pages you want it to effect.
Hm….. Sorry David!
I Imported the template from Envato templates and didn’t noticed that it was using the Elementor Canvas.
I also want to merge the header with the main container and make header transparent so content of the main container shows behind it.
You have instructed me about that here https://generatepress.com/forums/topic/main-navigation-use-container-background/
but I guess now with “Elements” those instructions are deprecated.
For a merged header:
Set the Colors you want for Sticky in the Customizer > Colors Primary Navigation.
For the static merged header set its colors in the Header Element > Site Head tab > Navigation colors