Lightroom stuck in full screen and won't transfer images to PS since upgrade

[SteveLowreyPhotography]

I seemed to upgrade PS - LR and my Mac all at the same time.

Now LR is stuck on full screen and I have tried all the shortcuts. I can't even transfer an image to PS.
I uninstalled and reinstalled my LR and then found I didn't have any pictures, thankfully I got them back by changing the catalogue. 
All my updates are up to date but I am well and truly stuck.

[SteveLowreyPhotography]

Just discovered I can not export images either - kill me now- how do I run a business?

[Rob_Cullen]

@SteveLowreyPhotography   [SHIFT+F] might toggle the screen through the different modes.

Cannot Export?  We will need a lot more details to help you diagnose this one.

Could be Disk/Folder Permissions, or 'Missing' images in the Catalog, etc.

Please include the following in your question:
Adobe product and Version number.
A Screenshot of the info panel from MENU: Help/System Info...
Operating system and Version number
The full text of any Error Message(s)
What you were doing when the problem occurred
Screenshots of the problem.

[SteveLowreyPhotography]

Okay, so I have fixed this.
The full-screen error was caused by a tick appearing in windows>screen mode>full screen

I have no idea how full screen was ticked but as soon as I ticked normal it rectified.

The inability to export images to Photoshop or desktop was a folder issue and a duplicate folder had appeared.

I merged this with the correct folder and it's back to life.

This article was beneficial 
https://www.lightroomqueen.com/lightroom-photos-missing-fix/. 

Thanks to everyone who showed an interest and offered to help.

[Conrad_C]

It might not be full screen, it might be a different problem. What do you see across the top along the right, is it:

(A) Library, Develop, Map, Book, Slideshow, Print, Web

(B) Normal, Live, Locked

If it’s (B), what’s really happening is the notorious and still unresolved Lightroom Classic issue of the Secondary Display window completely covering the application window. To hide it and reveal the normal application window, do either of the following:

Choose Window > Secondary Display > Show to deselect that command

or

Press Shift+E

If that isn’t the problem, more troubleshooting will be needed…