I am having this exact same issue, but with the Desktop version of Quickbooks for Mac 2021.  In all previous versions, once I downloaded and opened a .qbo file, the transactions would automatically match themselves.  On this version, it doesn't recognize any transactions and I have to manually highlight my QB transaction, then highlight the downloaded transaction of the same amount and then hit Match.  The process is extremely laborious. Is there a way around this in the Desktop version?