Well, after going over the documentation it appears to me that when it comes to how the button should appear, the rule is that there is no rule.
However, there are a few things to take note of per their docs:
- Avoid using floating action buttons for minor and destructive actions.
- Affirmative actions are placed on the right side and continue the process. Affirmative actions may be destructive, like “Delete” or “Remove.”
Other than that, you're free to style your buttons as you wish.
Now, personally, I believe destructive behavior is always something you should treat with special care by either asking the user to confirm their action or allowing them to undo it. Of course, that has nothing to do with color. When it comes to the appearance of the button, I think common conventions apply, which has been discussed elsewhere on this site.
I would argue that the guidelines imply using the secondary color is what you should do. The screenshot you used for the pizza app shows the secondary color for uninstall (which is a pretty destructive behavior) for both the good and bad options when pondering if you should add a background to your buttons.
Thus, my vote is for option 2 (most of the time): button with the secondary color as background