Why clicking on some apps on the dock does not open them?

Thanks for getting back to us, gxhxoxsxtxfxm. It's appreciated. Since the mouse is new, I have more steps for you to use that will focus on your iMac itself.

Reset the System Management Controller (SMC) on your Mac -- Reset the System Management Controller. Follow the steps under "How to reset the SMC on Mac desktop computers". Test the issue once you're back to the desktop.

Use safe mode to isolate issues with your Mac -- If resetting the SMC didn't correct the issue, test how it responds in safe mode. If there are no issues, reboot normally and test again in your own user account. Remember this when booting in safe mode: Limited graphics performance in OS X recovery or safe mode

How to test an issue in another user account on your Mac -- If the issue is also happening in safe mode, use this article to create and test another user account. This will demonstrate if the issue is isolated to your account, or if its system wide.

Let me know how that goes.

Take care!

Allow me to suggest a different approach: instead of going to the Dock, try using Command-tab to switch applications. It is so much faster.

Hey, gxhxoxsxtxfxm.

It appears that you're having an issue between your Apple wireless mouse and your iMac. Intermittently, it's taking two clicks on your mouse to open an application. I'm happy to help.

macOS Sierra: Change the way your mouse works -- Make sure that the settings are correct for how you wish your mouse to react.

If your Apple wireless mouse, keyboard, or trackpad isn‘t working as expected

Your mouse or keyboard intermittently stops responding

Follow these steps if your mouse or keyboard sometimes stops responding temporarily.

Click or press a key

Click the mouse or trackpad or press a key on the keyboard to reconnect the device to the computer. It might take a moment for the device to respond.

Check for signal interference

• Wireless networks that operate on 2.4GHz may cause interference. Move cordless phone base stations, microwave ovens, and other 2.4GHz electrical devices away from your Mac if you suspect interference.
• Keep wireless devices within 10 meters (approximately 30 feet) of your Mac.
• Avoid putting metal objects between your wireless device and your Mac.

Let me know how that goes.

Take care!