This article shows you how to disable the Android device checker which automatically fills in the words it "thinks" you want to type.
Steps

Step 1. Open the "Settings" application
This is typically a gear icon (⚙️), but it may also contain cursors.

Step 2. Scroll down the page and select Language and input
You can find this button in the "Device" section of the menu.

Step 3. Tap the active keyboard
It likely is Android keyboard or Google keyboard.

Step 4. Tap the Text Prediction button
You can usually find it in the middle portion of the menu.

Step 5. Move the "Auto Replacement" slider to the "Off" position
The cursor turns white.
- On some devices, you have to uncheck the box instead.
- This feature may reactivate after an OS update, so you must manually disable it again.

Step 6. Press the "Home" button
At this point, the text you type is no longer automatically corrected by the device.