Preview does not work

Hello supporter,
I try to add a campaign, but when chosing a style and clicking on “preview”, the new page is totally blank and so the whole process of creating ends here… ??

Plugins which are responsible for caching are switched off, the Lazy Load option is switched on… refreshing the site does not work…the support forum does not have this as an issue… FAQ and preview question is aiming to another issue…
now I am at the end of my solutions…
Thanks for help here!
Best wishes