I've been doing it pretty similar to you, and it's working.
My screen doesn't have any lines saying "Downloading and caching simulation driver..."
Make sure you are *logged into R18* using Chrome.
I use Firefox generally but I think the original steps I read said to use Chrome so I do only for this. I remember one time I inadvertently went back to using Firefox and it stopped working.
Try renaming your cookie file to simply "cookies.txt" (don't know if that is necessary but I've been doing that).
Also remember periodically you may need to download a fresh cookies file.
I don't know if any of these suggestions will help.
My problem is the download is painfully slow. Generally about an hour for 1 item. Longer for larger files. So I joined Patreon to support the developer to try to get a more current version than v.1.7.3. So far no luck with that. I'm waiting for the developer to tell me the password to unlock the newer versions after I download (and also to tell me what version is recommended for better download speed).
Good luck!