I get a 404 error message when using the downloader application.

Not at all. I'm not sure what you are referring to by the steps right before, but simply, I use a Blogger post I edit with Dropbox links and access them via Android devices to download and install. It's been working for a decade, perhaps. The files are all saved with the format as changed perhaps two years ago: https://dl.dropbox.com/scl/fi....etc... and end with "&dl=0", no longer needing to change to a "1". Every file on that Blogger page produces the 404 when attempting to use the Downloader application, while every file that is linked externally, not on my Dropbox, works fine. Not sure if this is what you wanted or if there's anything else you need. Thanks for asking. [P.S. I failed to mention that as Downloader is just a browser, I have tried two other browsers with the same result. Alternatively, I can properly download my Dropbox files with the Dropbox application.]

Second edit: I just uploaded the latest version of Kodi 21.2 to my Dropbox. A legitimate front-end file that has been tested and retested and is clearly free of any malware, and yet I just got the message that I've been shut down owing to malware, the instant I uploaded the file. I imagine this is behind my whole issue, and it's absurd. Every file has been tested with two different virus testing applications.