Hi there, its me again
So, I looked at your screenshot and as I understand it, the first line shows the file that is permanently moved with a redirect 301:
This Url would be https://your-site/wp-content/uploads/2020/01/quet-bg.png
However – just as you say as well – that file returns a 404, and not a 301.
This is also evident in the very second line of the screenshot where the same file registered a 404.
Thus, that report is “wrong”.
If it were a 301 permanent redirect if would indeed redirect somewhere else, and it does not. It is indeed a 404, as the file does not exist. Something else is pointing to that file, a post body perhaps (see later instructions how to remove it)
I know this because I use 301s a lot. For example, when you have a post that is already indexed by Google and then you make a change to its URL, you will have to 301 the old URL to the new URL.
That makes sure that Google doesn’t assume a 404 and hence continues visit that post.
And hell, those 301s can be “sticky”!
Not for nothing they are called “Permanent redirect”.
Sometimes, I have to remove a 301 and it takes like forever to be recognised by google that the post is indeed gone for good now. I am still waiting on some to be recognised as fully removed by Google.
So the only thing I can imagine here is that the tool you use for SEO Scan is not updated with the latest data from you site and perhaps you have had a 301 on that file some time ago but not anymore.
You can decide here to either ignore that, or re-instantiate the 301 in your .htaccess or via plugin to redirect the URL somewhere else (to an existing place), which won’t slowdown your site at all, it will rather ensure that no 404s exist in your site.
If you still include that URL in some posts you can find out quickly with a Database search or using a search and replace plugin like “Better Search Replace” – if there is any post that has that URL in its content or else, the plugin or database search will return it in the results and you may then adjust that.
Note, if you want to ensure (if the file is truly not used anymore) that Google does not index it anymore either you can use the tool here https://search.google.com/search-console/remove-outdated-content to request full removal of that URL from the engine. However I would suggest to ensure the file really is not needed anymore elsewhere first (which may be the case) using the above described search and replace or database search methods.