Sorry to hear you are running into this issue. Tryingh to understand if you are missing entire project files or content/style within a project (or both). In the former case, please check the earlier response from @Claire Park
If your content/style got affected, could you please share screenshots comparing the two versions. The previous version can still be found in a folder called [Originals], but is available only for donwload, not for editing.
Just to be clear, your previous designs that have been migrated to the new version will still remain editable, but using the new version of the app. Please feel free to ask any questions you might have about using the new version: it offers a lot of new functionality and the interface will become familiar as you start using it.
And as asked previously, if you have concerns about lots style/content, please share screenshots. If you prefer, you can send a private message by navigating to https://community.adobe.com/t5/user/viewprofilepage/user-id/11927426 in your browser and clicking the Message button (make sure you are signed in with your Adobe id)