First, you have to convert your file to the latest update since your QuickBooks Desktop Pro (QBDT Pro) version is 2016. Then, subscribe to QuickBooks Online, import the transaction from the QBDT Pro 2020. I'd be glad to walk you through the process.
Step 1: Convert QBDT Pro 2016 to QBDT Pro 2020.
To have it successfully converted, you have to use a trial version. Export your company files from QBDT 2016 then import it to QBDT 2020. Then save your transactions.
Step 2: Import transactions to QuickBooks Online from (QBO) QBDT Pro2020.
Upon setting up your account in QBO there will a checklist for you to upload all the files. I added a screenshot for your reference.