I don’t mean the browser cache of the device, but the cache on the server. If you have a plugin for the cache, or the server itself has a caching system, it has to distinguish between mobile and desktop.
If you build the server cache visiting the page on desktop and the caching system doesn’t distinguish between mobile and desktop, when you visit again the page, e.g. using a tablet, you see the cached page that was generated visiting the page using a desktop.
In any case, using a tablet simulator I see that it works.
Try with your tablet visiting https://energoaudit.sk/clen-apes/?no_cache=1
and let me know if you still see the desktop version.