I had to force restart the computer, and when I reopened the project, I found that Unity didn’t compile the latest scripts, even though I had modified the script content.
Crashes, forcing the task to end, power outage and so on … if any of these leave your project in a murky state, close the project, delete the Library folder, wait till its complete, and then try again.
Also good practice when upgrading the editor and something seems fishy.