I recently switched to the next gen studio ui preview and for the second time I had a problem with the toolbar disappearing and I couldn’t find any way to solve this problem other than disabling this beta feature and re-enabling it.
Is there any other solution to this problem? For example, a keyboard shortcut.
The toolbar disappeared after restarting the roblox studio ( I closed the studio using the keyboard shortcut alt+f4)
You can get the top bar back by double clicking any of the tabs like “Plugins” for example.
Hope this helps! 
It didn’t help.