MacOS – way to show if I have more than one Google Chrome window open in the Dock

If you try to make a window bigger than the size left by the Dock, by dragging the bottom of a window yourself, you will notice that you can't do it. This is because the Dock already behaves like a Windows Taskbar: you can move windows behind it but not resize windows beyond it.

The problem lies with the tool that you are using to resize the window-it is extending the window more than it should do. Try using a different tool to do the resizing or resize the windows yourself.

There's a Multi-Touch gesture that can show you all the instances of one app. Swiping downwards with either three or four fingers (configurable in System Preferences > Trackpad > More Gestures) opens "App Exposé", a handy birds-eye view of all your open windows in the frontmost app. It's not the same as an indicator in the always-present Dock, I know, but I think this can be one of the best options you'll get without 3rd-party software (assuming such software exists).