Cura 5.1 won't open on a Mac

[ShopGeezer 2]

So I run Cura on my Windows laptop and my desktop Mac. Both versions of Cura are older so I decided to update both computers to version 5.1.  The laptop updated easily and runs 5.1 just fine. The Mac updated and opened the new version of Cura but then the OS flashed up the usual banner saying that this was a file downloaded from the internet and did I want it to open. I said yes and Cura disappeared and won't open at all when I try again.  I have uninstalled and reinstalled Cura 5.1 three times now. Each time Cura opens and the Mac flashes up the internet file warning and each time I tell the Mac to open the file Cura disappears.  

 

I know the solution is don't use Macs but it is very convenient to have Cura installed on mine so I can work on files in the house. The laptop runs the printer out in the shop. Any other Mac users noticed this behaviour?  I have run many versions of Cura on this Mac. Never a problem before. I've downloaded a lot of software. There is always the warning banner about a file from the internet but I have never seen this problem before. Maybe Apple should get with the current century. All software is downloaded from the internet these days. There are no nice little boxes with a CD in them anymore. 

 

 

[ShopGeezer 2]

Found this after a search:

 

https://support.ultimaker.com/hc/en-us/articles/360013828939--Ultimaker-Cura-can-t-be-opened-because-Apple-cannot-check-it-for-malicious-software

 

I have an older version of the Mac OS (10.13.6, High Sierra) but I suspect it is the same problem. The Mac can't check the program so it won't open it. The work around shown in the help article doesn't work for me.  Has this been addressed in the new Beta of Cura 5.1?

[Smithy 1,144]

I am using Macs for decades and don't have problems with Cura. 

Are you downloading Cura from Ultimaker?

Try to right click the install file and then open, to see if that helps.

[ShopGeezer 2]

I have used Cura on this Mac since early version 3.1 and never had a problem upgrading to newer versions. Version 5.1 is the only one that is causing problems. I think it is something like the issue described in the support document above. For some reason the Mac is unable to check the file for malicious software so it blocks Cura from opening. My version of Cura 4.13.1 still works just fine. Version 5.1 will not open in any way including left click open or any other method. The Mac can't seem to check the file so it is blocked from opening. 

[Smithy 1,144]

Really strange, I am using 5.1 and it is working without any workarounds.

But I am on the latest MacOS, so maybe thats the reason.