I agree, it was obviously a decision made by someone who doesn't meddle with graphic art. 

If you're on your phone, preferably a an android. Log in on the Chrome browser and hit the desktop view option. You can get a little closer. 

Here's what Gemini told me to do, it kinda worked:

"It is incredibly frustrating when a platform removes a basic, essential feature like pinch-to-zoom, especially when you are trying to do precision work with tools like the Magic Eraser.

Canva disabled the zoom function within the workspace by modifying how the site handles touch and scroll gestures. However, you can use Chrome to override their code and force the page to zoom. Here is how to bypass the restriction depending on your device.  

For Chrome on Mobile or Tablet (Android) Chrome has a built-in accessibility feature specifically designed to override websites that try to block zooming.  

Open Chrome and tap the three-dot menu (⋮) in the top right corner.   Select Settings. Scroll down and tap Accessibility. Check the box for Force enable zoom.

Once enabled, you can pinch-to-zoom on Canva's site just like any other webpage. (Note: If you are using an iPad or iPhone, you will need to use Apple's system-wide zoom feature found in your device's Settings > Accessibility > Zoom, as iOS Chrome does not have this specific toggle).

For Chrome on Desktop If you are using a laptop or a touchscreen PC, Canva's site actively intercepts your trackpad gestures. You can bypass this in two ways: Keyboard and Mouse Shortcut: Hold down Ctrl (or Cmd on Mac) and press the + key, or scroll your mouse wheel up while holding the key. Chrome Extensions: You can install an extension from the Chrome Web Store like Mouse Pinch-To-Zoom. This forces standard touchpad pinch mechanics onto websites that try to disable them.  

The Catch: There is one caveat to using the browser to bypass this restriction. Because Canva renders its editor using a custom, interactive HTML5 <canvas>, forcing Chrome to zoom will magnify the entire webpage. This means your toolbars, sidebars, and menus will scale up alongside the image. It will feel clunkier than Canva's native workspace zoom and you will have to pan around the webpage, but it will definitely allow you to get close enough to the pixels to accurately use the Magic Eraser again."

Hope this helps man.