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