I found a solution, quite by accident I must confess
The problem seems to be with the new "Welcome Page". If you uncheck the box that says "Show on startup", your IDE should revert back to it's normal settings.
Hope this helps
P.S. Please mark responses as helpful or correct if it proves to be either
Welcome! This space is for questions related to Oracle Enterprise Manager, and it appears you're asking a question about SQL Developer.
In the ACTIONS menu on the right, you should be able to click on "Move", and then specify the correct space, such as SQL Developer , so that the appropriate experts can see your question.
There are tips on how to find the correct space on the Getting Started page, which also has instructions on how to change your display name so you're not just a number.
Thanks and good luck!
Thanks for your help. Your solution fixed my problem.