Hello, Lizpru,
I appreciate all of your efforts to bring in your transactions into QuickBooks. I'll share something about the supported file format when uploading the old bank transactions.
QuickBooks Desktop only supports the .qbo format when importing your old bank transactions.
You'll want to go to your bank's website and check to see if they have an option to let you download the .qbo format instead.
If not, I would recommend looking for converters that let you convert your .csv file to .qbo. Alternatively, there might be a third-party app in our Desktop marketplace that lets you do this.
You can go to this link to look for one: https://desktop.apps.com/home.
You can find more details and a quick guide about getting your bank transactions to QuickBooks: Download Bank Feed transactions in QuickBooks Desktop.
You might also find this article helpful if you run into obstacles while importing your file (after converting to .qbo format): Fix Web Connect import errors.
After getting all of your old bank transactions into QuickBooks, you can start categorizing them.
I'm up and ready to help you out again if you have questions about the common processes in the Desktop platform. Leave the details on what you want to achieve and I'll get back to you.
