Tried many times to transfer all my data from my Desktop Enterprise 21 to online with no success.

Where is your company located? US or another country?

You can use the trial version of QB Desktop 2024 Enterprise to upgrade your data and convert it to QB Online US version. Check your company file first before converting it to QB Online. If your Total Target is > 350K, you will have to convert your data to QB Online Advanced. Run the Condense Data utility to lower the Total Target size if you prefer converting your data to QB Online Plus or a lower plan. You can use the trial version of QB Desktop Enterprise for good to access your historical data later.

Hello, @simon96.

Since your Desktop version is 2021, we can move your company file to QuickBooks Online with an online tool. This tool is for QuickBooks Desktop company file versions 2011 and later.

First, select the link for your QuickBooks version:

• QuickBooks Pro/Premier
• QuickBooks Enterprise
• QuickBooks for Mac

Here's how to upload after you click the link: 

1. Click Get Started, then sign in with your Intuit Account.
2. Select a file or drop the company file inside the Upload box.
3. Click Open to upload the company file; we'll automatically update it to the latest version of QuickBooks Desktop.
4. You'll see an option to move to QuickBooks Online.
5. Follow the on-screen instructions to guide you through when you move to QuickBooks Online. 
    

You'll receive an email saying "Your company is now Online" when the migration has been completed.

In addition to the first resolution I provided, I also agree with SIAB’s suggestion to use the QuickBooks Desktop 2024 Enterprise trial.

Please visit this article to learn more about moving your QuickBooks Desktop file to QBO: Move your QuickBooks Desktop company file to QuickBooks Online.

Please let us know if you have any other questions.