Mobile template showing on desktop

When i go to our site: http://www.saarmagazine.nl
most of the time it shows our mobile template in stead of our desktop desktop homepage. The desktop homepage shows a grid of three recent posts, dhe mobile template shows one large post. Next to this it doesnt show the logo and menu header on desktop (when it shows the mobile layout).
Also when I go to a blog from the website on my desktop, it shows the mobile layout for posts in stead of the desktop layout. So the image shows smaller and the text is on the left side of the screen and very narrow. Also without logo/menu header.

When i do a hard refresh on that page it seems like the cache erases so i get the right version, but my colleages never get to see the right version.

Here you see the mobile layout showing on a blog desktop (just showing the top of the page), + missing logo and menu and text on the left side):
https://www.saarmagazine.nl/wp-content/uploads/2023/12/Scherm­afbeelding-2023-12-04-om-14.59.41.png

Here you see what it should look like (image showing entire page):
https://www.saarmagazine.nl/wp-content/uploads/2023/12/screencapture-saarmagazine-nl-ik-wil-zeggen-tegen-vrouwen-die-wel-kinderen-hebben-2023-12-04-15_02_59.png

We’re already usng WP super cache.

And I also tried the Newspaper Mobile Theme, but the same problem appears. I hope you can help me!