Thanks for becoming part of the Community, João Nascimento. I appreciate your detailed information and screenshot.
I tested this myself in our test drive account and was able to locate my Customize button next to the Print or Preview and Make recurring options.
Here's an image showing my experience:
Since your estimate creation/editing screens aren't showing the Customize option, I'd recommend checking your browser. It's possible this could have something to do with temporary internet files. Browsing applications store these types of records, but sometimes they can cause issues with certain webpages. You can open a private window and check to see if the button displays.
Here's how to access incognito mode in some of the most commonly used web browsers:
In the event it continues occurring while using incognito, you'll initially want to try switching to another browsing application.
Here's a list of supported browsers
Google Chrome - version 78 or newer
Mozilla Firefox - version 76 or newer
Microsoft Edge - version 75 or newer
Opera - version 68 or newer
Samsung - version 10 or newer
Safari - version 12 or newer
You can also check a browser's compatibility with your books by utilizing our browser health checkup tool. QuickBooks supports the current and two previous versions of browsers. If you find that you're using an older version, make sure to update it to its latest release. Steps for doing so can be found on the particular company's website.
In the event you've found no problems that could be causing this with your browser, I'd recommend using a different device and/or internet connection. If it continues happening on other devices and/or internet connections, you'll want to get in touch with our Customer Care team. They'll be able to pull up the account in a secure environment, conduct further research with you, and create an investigation ticket if necessary.
They can be reached while you're signed in.
Here's how:
Use your Help (?) icon.
Click Contact Us.
Enter a description of the situation in your What can we help you with? field, then hit Let's talk.
Select Start messaging or Get a call.
Be sure to review their support hours so you'll know when agents are available.
I've also included a detailed resource about system requirements which may come in handy moving forward: System requirements
I'll be here to help if there's any additional questions. Have a wonderful Wednesday!
I appreciate you for trying the steps suggested by my colleague.
You may want to check your access as a user. Users with limited access to QBO can't customize forms. Admins should have the option to customize estimates.
If you still don't have the option despite being an admin user, I recommend contacting QuickBooks Online Support. Please follow the steps below to contact support:
Sign in to your QuickBooks Online company. Click Help (?).
Choose an either tab to get started: Assistant or Talk to a human.
Search or select Contact Us.
Start a chat with a support expert.
You can contact us from Mondays to Fridays, 6 AM to 6 PM PT, and Saturdays, 6 AM to 3 PM PT.