I connected a bank account and it only downloaded 24 transactions

Hello there, kaytoll1.

The number of transactions that QuickBooks Online will download depends on your bank. Though, we can manually import your last year's bank transactions. Log in to your online bank account to get a web connect file. You can use either any of these file formats: CSV, QFX, QBO, or OFX.

Then, let's follow these steps on how to upload it:

1. Go to the Banking tab.
2. From the Update drop-down, select File upload.
3. Click Browse and select the web connect file from your bank.
4. Follow the on-screen steps in mapping the data.

I have an article here for your reference: Manually upload transactions into QuickBooks Online. Also, this link will show you how to categorize and match online bank transactions.

Please post again if you have other concerns. Have a great day!