The button still exists, you can see it in this topic : Events Plugin 📆
If you changed some settings recently, you probably need to wait a few days. If you have a custom theme, it may hides this button, you can try yourforum.com/safe-mode to deactivate your theme and check if it appears
You can activate the summary locally on every topic, it may help to check what posts meet the criteria : https://meta.discourse.org/t/summarize-this-topic-button/132790/?filter=summary