Hi!
First, it's not sure that the 32 bit-version will remain and become stable, as the Opera team in Oslo has been shut down, and now the browser is being developed in Poland, but I hope they will continue support it.
So, regarding the extension page problem; I have the exact same problem that you have. And it was totally random for me, sometimes it worked, and sometimes it looked exactly as it does on the image you provided. But now I think I know what's causing this:
http://dev.opera.com/addons/extensions is broken
http://dev.opera.com/extensions works fine (without "addons/" in the url)
For me it is like this: When you use the first link (that leads to the broken site), you must use Opera developer or beta. If you use Opera stable, firefox, chrome etc, it will just direct to the working (http://dev.opera.com/extensions) site.
Can someone confirm this?