Contacts don't display & drop down windows show outline but no text contents

Did you restart your mac?

If the problem persists after a normal restart, restart in Safe Mode.

Do things work in Safe Mode (despite being slow, which is normal)?

Download Etrecheck, run it and post its full report here.

As an aside, using contacts in icloud.com is as simple as going to icloud.com, logging in and clicking Contacts.

But you should do as above to try and restore normal functionality of your mac.

There are several issues with this mac.

Battery failure - Your battery is reporting that it needs to be serviced.

Unsigned files - There are unsigned software files installed that could be malicious and should be reviewed.

Security updates disabled - Security updates are disabled. This computer is at risk of malware infection.

Apple security disabled - Apple security software is disabled. This computer is at risk of malware infection.

The first thing is to uninstall cleanmymac.

You will have to follow their instructions for it. It is not enough to drag the application to the trash.

If you plan to keep this mac for some time yet, consider replacing the battery. A dying battery can cause crashes and if it starts to swell, it can impact the use of the trackpad and make it erratic.

You should reactivate the security updates. These are separate from the general OS updates.

In System Preferences->Software Update, click Advanced

You should post the report here.

Select Share Report->Copy Report

then in a reply here click the Additional Text button below your message and paste into the text box.