Thanks for the checklist! I don’t get the error when working with the course plugin. I did get it when trying to rename the course plugin, similar to the other user. And now I’m having the error in my own plugin. Everything else looks good: block exists, Gutenberg installed, render function exists.
Here’s a zip of the plugin I’m working on for reference. It should throw the error on activation. To fix the error, you can comment out register_block_type in src/custom-post-types/cpt.php, where I have the render function as well. I don’t expect you to review this plugin or spend a bunch of time hunting down a bug, but might be helpful if it turns out to be a common issue.