elementor OR plugins, can’t use both

Hi,

I did my best to be as brief and specific as possible. Please read to the end and look at the 6 images I “attached”. Thank you so much!

I installed OceanWP on localhost xampp and did this:

updated wp to 5.0.3
installed OceanWP theme, activated it
installed OceanWP extra, ran updates
installed OceanWP child theme, activated it

created menu with 3 pages (welcome, blog, courses)
added css code to put white border around entire website
added css code to change the background color of every page
edited the OceanWP settings for every page

installed latest version of elementor and added column section with a fixed image at the top of every page (under the header). images A1, A2, B1, C1 show exactly what I want them to look like.

Installed LearnPress instead of LifterLms (thought it might be the cause of the problem detailed next) and image C2 happens. My “design” is gone.
I tried to edit the page somehow and checked “pages” in the dashboard (D1) where you can clearly see that LearnPress adds and creates its own pages and that’s intentional, I think. But then I tried to edit the courses-2 page (D2) and tried to at least change the background colour in the customiser the result is visible in C2 – nothing happens: I cannot edit the page with the plugin (Learnpress, LifterLMS, Woocommerce ect……) in the customizer and elementor doesn’t load for that page.

all mentionend images are here: https://imgur.com/a/8SARXOF

So, do I need to sort out the pages to solve the mystery? (I have no idea how)

For some reason I can either edit my pages with elementor adding shortcodes for everything (which is tedious and I can’t always do, I am forced to use woocommerce with 2 more addons) OR
I don’t use elementor and I can use the plugins. But then the pages look sh**.

What’s the problem?

Thank you so much,
Martin