There are available slots on my calendar, but they are not appearing on the Provider Portal Dashboard calendar preview

Check calendar event settings
Ensure your availability is correctly set on your calendar. If you have an event on your calendar, set the status to "Free" in order to make the slot available.

Sync and refresh
Wait a few minutes for your calendar to sync with the system, then refresh the page

Check the calendar account connected
Ensure the correct Google account or Outlook account is connected to the Provider Portal. If needed, change the connected account. Refer to these articles:

Check your timezone settings
Make sure the timezone of your connected calendar matches the timezone set in the portal. Both should have the same GMT offset so your availability displays correctly.

Reconnect your calendar

In many cases, simply reconnecting will resolve any calendar connection issues that may have occurred. Refer to I want to reconnect my calendar