@leocg To you and anyone reading this at a later time: maemo.org seems to host a bunch of old software. I was able to source Opera Mobile 12.1 from there!

As per this article: https://dev.opera.com/blog/opera-mobile-10-for-nokia-n900-n800-n810-maemo-standards-support/

Opera at least used to support Nokia N900 - where can I find the latest version? The link in the article is broken.