Thanks for being a part of the QuickBooks Online family! We've been making some changes to the way QuickBooks Online looks, including moving some buttons around. Don't worry, the shortcuts you're used to are still available, just in a new location. I'll help you find it.
Previously, the (+) icon was in the upper right, alongside the magnifying glass, gear, and (?)Help icons. Now, it's moved over to the left-hand menu and has been renamed +New. Here's a screenshot to show you where I mean.
When you click that button, you'll see all the same shortcuts as before, including Estimates. Keep in mind too that you can create Estimates from the Sales section as well. Here's a look at the menu.
That should get you back on track! I'm here if you need anything else.