Currently, you have a subpage that is named /blog - therefore, it is not possible to name the collection “blog” because then you would have two pages with the name “blog”.
A good workaround would be to name your blog collection, for example /ausare-blog or rename the page /blog to something else like /ausare-blog .
It should still be possible to give menu item the name “blog” though. That could be a nice workaround.
Thank you for your explanation. I will think about the right name to use but for now I will leave it like it is since I have understood the fact that there will necessary have a text after the domain name regarding the name of the collection.