Most questions about Visuel have the same short answers.
No. There is no sign up. Your data lives in your own iCloud.
On your iPhone and in your personal iCloud. With iCloud switched on it syncs by itself.
Sign in with the same Apple Account and turn iCloud on. Your workspaces come back on their own after a short moment.
Check that the phone is online and that iCloud is switched on for Visuel in Settings. Syncing can take a minute, and reopening the app gives it a push.
Contact: support@visuelapp.com