It seems that all I had to do was following Mate's suggestion but make the edit in the env file, not env.example. (I had used the search feature in VSCode to find all instances of SESSION_DRIVER but the only one of the three hits that set the value of SESSION_DRIVER was in env.example; env didn't show up in the search result at all! I don't know what that is but as soon as I saw env and changed SESSION_DRIVER there, I was able to bring up the Laravel 12 default page.

I'm really annoyed that the course creator didn't preclude this problem by having students edit the env file before they tried to launch the app.