Hi Christy,
Thanks so much for reaching out with your BoldGrid Post and Page Builder questions.
It’s generally not recommended to run two page builder plugins at once as it’s been known to cause slow downs and conflicting code, but I do understand the need to do so in some instances.
One thing you could try is temporarily deactivating Elementor, then see if WordPress again allows you to select Post and Page Builder as your primary page builder.
If you use the classic WordPress editor you should be able to switch your default page editor from that screens “tools” option. Here’s a guide on setting Post and Page Builder as your preferred editor in WordPress.
I hope this helps!