Hello there, @rikis981.
Please allow me to join the thread and help share additional information about the opening balance when reconciling transactions in QuickBooks Online (QBO).
For you to have the opening balance, you have to go back to your credit card account register and manually mark the transactions/the opening balance with R under the Check-Mark (✓) column.
You can see attached screenshot for additional reference.
Please know that I'll be always here to help you if you have any other banking questions, just add a post/comment below. Have a great day ahead!