Mojave won't allow me to drag n drop or export from Photos

Download and run Etrecheck. Copy and paste the results into your reply. Etrecheck is a strictly a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance. No personal information is included in the report.

Applications are not working use etrecheck https://etrecheck.com/

And post the results , also create a new test user account and monitor it How to test an issue in another user account on your Mac - Apple Support

In this account are you able to run photos , games application .

The method to export photos from photo library to desktop is hold command key and tap the desired photos to get selected - click on export photos - again click on export in the next window , a window opens click on desktops in the side bar - and again export the photos are exported on the desktop .

But in your case it is not happening then photo library is corrupted you can see these articles How to use the Photos library repair tool - Apple Support

And don't use third party apps / softwares in Mac or even to clean duplicate photos see this article Using third-party apps to remove duplicate photos might damage your Photos for macOS library - Apple Support

If the applications are not opening or quitting repair your disk Repair a disk using Disk Utility on Mac - Apple Support

And not sure what is PicMonkey is it a third party app ? if you wish you can post the screen shot of applications that are running in your Mac also don't any any anti virus , some cleaners they will corrupt the Mac .

You don't need to purchase anything to post the report. After running Etrecheck click on the Share button, select Copy Report and paste the report into your reply here.

What happens when you try? And FWIW, when you have more than one question you should create a post for each.