I would try running the Mac installer from the command line, and seeing if there are error messages.
Note that there are special instructions for Mac Catalina
There are other ways to save besides Timimi. There's the default HTML5 saver. There is TiddlyDesktop. You can run your files using a webdav server (I understand there is a webdav server already on Mac. But if not, there is Rclone that can run as a webdav server).