On my iPhone, my most used keyboard feature is probably undo. Sometimes, it's the fastest way to start a sentence over and try again. iPhones have a systemwide undo option (just shake the device and you'll see it), but I miss that when I'm using an Android. Luckily, it turns out that Gboard for Android, which comes standard on Pixel phones and devices running stock Android, has a hidden undo key.
How to use Gboard for Android's hidden undo key
To use your device's hidden undo key, you'll need to add a Japanese keyboard to Gboard for Android. For some reason, this is the only language that ships with an undo key built in. Here's how to install it:
Go to any app where you can see the keyboard on your Android phone. If you have Gboard installed, this should reveal it.
On the keyboard, hold the globe key until you see a pop-up.
Select Language settings. This button may have a slightly different name on your device.
In the language settings page, select Add keyboard and search for "Japanese."
You'll see different options for keyboard layouts. Select the 12-key layout and tap Done.
Now try typing in any app on your phone. When you're done typing, hold down the globe key and switch to the Japanese keyboard. You'll see the undo key in the top-left corner. To switch back to your default keyboard, hold the globe key again.
While this workaround is slightly inconvenient, switching between keyboard layouts is fast enough to make it worthwhile, at least for me.
Your phone may not come with Gboard installed. If that's the case, you can install it here. However, some manufacturers build a systemwide undo key into their Gboard replacements, which would make this trick unnecessary. On Samsung's default keyboard, undoing something is as simple as swiping left with two fingers.