Some time ago it was possible to specify the category of an idea on creation (GUI "Submit Idea").
At the moment this is no more possible. You have first to submit the idea and then edit it and add the category.
This is related to a platform-side defect, and we're continuing to work with our platform provider's engineering team for resolution. Thank you for your patience here!
To follow up here, the root causes behind this defect have been resolved. The dropdown options for idea cards (both in creating cards and for already-submitted cards) should be accessible by all users now -- if you are still experiencing issues with this, please clear your cache and cookies then try again, and thanks for your patience!
HEADQUARTERS|135 SW Taylor Suite 200, Portland, Oregon, 97204