Importing QBO files is part of the bank feed feature. You cannot use it on outdated versions of QB Desktop. You may have 2 options

1. Use TP Importer with your QB Desktop 2021. It's a $199 one time license and you can get it for free from a reseller.

https://get.transactionpro.com/bank_feed_alternative

2. Use the trial version of QB Desktop 2022 Enterprise as a workaround to run the bank feed feature.