After activating StartNext, you will see this notice:
Click Begin installing plugins. You will be navigated to Install Required Plugins page.
Simply check all of them (or all of required plugins and some recommended plugins you like) and from the drop down select Install, then hit Apply.
If you want to use WPBakery Page Builder then don’t need to install Elementor Page Builder Plugin
If you want to use Elementor Page Builder then don’t need to install
WPBakery Page Builder Plugin
When finishing, it should look like this:
Next, go to Plugins >> Installed Plugins check all of them and from the drop-down select Activate and hit Apply
Required plugins: Elementor, WPBakery Page Builder, StartNext Toolkit, ACF Pro, ACF: Font-Awesome.
Recommended plugins: WooCommerce, Contact Form 7, Newsletter, Contact Form 7 and Unyson.