Allow me to barge in to this trend. Below are the steps how to manually upload bank transactions in your QuickBooks for Mac.
I've got you an article as a reference: Set up and use Online Banking (Mac).
Older versions of QuickBooks for Mac has the possibility of getting error when importing .QBO files. You might want to upgrade to continue using this feature.
On the other note, the bold and thin check marks that Jonpril_L is referring to are found in the register. Manually checking the entries will show bold marks. While the thin ones are for matched bank transactions from the online banking window.
Let us know if you have any questions. We'll be right here to help.