Thank you for the detailed information and the screenshot added. I can share with you some troubleshooting steps to fix the error you're getting. First, you can download and run the Print & PDF Repair Tool from the QuickBooks Tool Hub. It resolves common errors when you email forms through the software.
Thank you for sharing the result after performing the steps above, @chapii.
The article that my peer provided above is a great resource to help fix your issues with emailing statements. If you've already gone through each solution from there, you can uninstall and reinstall the program.
However, if the issue persists, it'd be best to contact our Customer Support Team. They can investigate the root cause of this and help you fix it. They are available from 6 AM - 6 PM PT (Monday - Friday) and 6 AM - 3 PM PT (Saturday).
Select QuickBooks Desktop Help from the Help icon at the top menu.
Click Contact Us.
Enter Error when emailing statements after performing the recommended steps in the Ask a question (or tell us what's wrong) box.
Choose either Start messaging or Get a callback.
The screenshot below shows you the steps.
In case your emails aren't using a template you created, visit this link for the solutions: Troubleshooting Guide.
Feel free to leave a comment below if you need anything else. I'll gladly help. Keep safe.