This seems to be a problem peculiar to Catalina (macOS 10.15.1). There is a fix, as Otared and Glen have indicated.

go to Apple menu -> Preferences -> Security & Privacy
on the Security & Privacy, login, choose the tab General
there choose, towards the bottom of that pane, under « Allow apps downloaded from: » 
                   choose the radio button App Store and identified developers
                   click the button «allow anyway»

The macOS still chokes when you first try to update lmtx , but this time it presents the option «Open». Select that and you are good to go.

So, thanks, guys.

And Mojca, yes, it is very confusing. Still, that seems to be all that one has to do make the download. So perhaps there is no need for changes at your end.

Cheers, Alan
                    

On Sun, Nov 17, 2019 at 11:30 AM Keith McKay <mckaymeister@gmail.com> wrote:

This is the standard way to install "apps" on a mac, which have an unknown developer, to Apple anyway. It is a bit annoying when it happens especially when one has forgotten that you have to go through the Preferences dialog to get it to run. In my case it's an age thing.🙁

Best Wishes

Keith McKay 

On 16/11/2019 22:27, Glen Helman wrote:
There seems to be a way around this built into Catalina, however awkward it may be.

I tried to install lmtx on a computer running Catalina that didn’t have an installation and received a similar error. (There seems to be a quarantine applying to the text of the script and not merely the file because I tried creating a new document with the same text and received the same response, and that response referred to the download of the original file.)

I did find that the “general” tab under “security & privacy” in the system preferences had, in addition to the usual two choices, a reference to the downloaded script with a button reading “allow anyway” (or something to that effect). When I tried to run the script again after clicking that button, the “developer cannot  be verified” dialogue included “open” as a choice; and, when I clicked that, the script ran successfully and the installation was usable.

I then tried the install script on another computer running Cataline where I had installed lmtx last spring. I ran into the “developer cannot be verified” response again, but the same workaround allowed the script to run, and the installation was updated.

Glen Helman

On Nov 15, 2019, at 4:36 PM, Alan Bowen <bowenalan03@gmail.com> wrote:

Though I was able to download the latest ConTeXt beta without any problems, my attempt to update my ConText-LMTX installation was blocked. The error message was

“mtxrun” cannot be opened because the developer cannot be verified
macOS cannot verify that this app is free from malware.
Safari downloaded this file on April 29, 2019.

 I am not sure why this is happening and wonder if it would OK to copy mxtrun from my ConTeXt installation and replace the version in my ConTeXt-LMTX installation with it.

Alan
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