I'll help you check the settings to ensure that the PDF Attached option is enabled, Yankeln.
Let's make sure to log in to your QuickBooks Online account using the regular browser. Then, follow these steps:
Here's a sample screenshot for a visual reference:
Once done, open your QuickBooks Online mobile app and try sending a sample estimate to your email. Then, check your email and open the estimate. You will see the PDF attachment at the bottom.
If you're getting the same result, you'll want to perform some troubleshooting steps. You can follow the instructions in this article: Troubleshooting Quick-Start Guide for the QuickBooks Online app.
Please let me know how it goes. I'm here to help you out again until you're able to see the PDF attachment.