1) the same blog post is saved twice on two different URLs, which creates duplicate content. (see urls in the screenshot)
It is saved under .../odlingstips/category/blogpost and .../odlingstips/blogpost
This can be fixed with canonical links and on a page there is the possibilty to add the canonical in the SEO header. yet on a blog post I couldnt find a SEO header (only SEO title and description).
2) the blog page ../odlingstips is also saved twice under /category/all
Can you advise how to solve this, please?
I would like the page and post with the SEO permalink
I'm not sure that there's a way to prevent that right now; you can add canonical links to standard pages by adding the meta tag to that page's Header Code field, though there isn't a way to do that with a blog post.
While tools like the one you used will give you a warning, I don't think it's really going to hurt anything in a real world setting.
Same problem... as usual, none cares and tells you to find an other way to do it...
Blog settings are so hard here, can't even duplicate an article....