Hi @eedee,
thank you for replying that fast.
After disabling all plugins but Gutenslider I renamed the images and refreshed my page.
The difference I noticed was that the images were not blurry anymore.
However the mobile slider was shown on desktop although it is deactivated (I double checked).
I then re-activated each plugin one by one which showed that “editorskit – Gutenberg page building toolkit” by Jeffrey Carandang somehow forced low resolution images to be loaded.
So I will keep it deactivated at first and ultimately will delete it.
Besides that, hiding a Gutenslider still doesn’t work.