More info: this is a Mac Mini M1. There are two accounts, mine and my wife's. My wife's doesn't have this problem, so it's not system-wide. That is, the speech synthesis extension is loaded. I must have done something. The problems all started around the time I did a brew upgrade. Could that be it?

I'm getting back into coding after years away. I ran into the same problem with the tutorial. I also spent a lot of time trying to debug javascript without a debugger, which you do with a lot of console() calls. Fortunately, Swift has print(). So I added a print(error) right after the catch after the decode() in ModelData, and the error was simply that I misspelled "latitude".