Hey Reece,
You could create a branch line from your Mainline and upgrade that branch line to any version 9 of your choosing. Then run the app locally and see if there are any breaking changes. There is a high chance it might break the UI elements especially if Atlas version gets upgraded so I recommend the approach I mentioned each time you plan to make a big mendix version jump.
Additionally, you could check out the release notes to see if you could spot what might break your app if you perform the upgrade : https://docs.mendix.com/releasenotes/studio-pro/
Hope this helps.
Regards
Kevin
Follow Kevin’s good advice. Best go to 9.12.2. Once you have upgraded and started using it, there is no going back with losing some data. You will get all the good stuff like better UI and styling options, Workflow, nanoflow-debugging and lots more.