How can I see if a synced Notion event from Google Calendar is recurring?

When you set up the automation for the first time, or you configure it after the onboarding, scroll down to Field mapping and then click on Add field to add the Is Recurring (Checkbox) option.

Then, map it to the compatible Notion field on the right (usually, the ☑ Done property).

If any event you sync from Google Calendar to Notion is recurring, this checkbox will be marked.