Can anyone help all drop down menus have become dark

Major Issues:
  Anything that appears on this list needs immediate attention. 
  Unsigned files - There are unsigned software files installed that could be adware and should be reviewed.
  System Integrity Protection disabled - System Integrity Protection is disabled. This computer is at risk of malware infection.
  More than one antivirus app - This machine has multiple antivirus apps installed.

So you have system security disabled, and more than one third party antivirus... the correct number being zero.

And I thought that weirdness reached a very high level with this:

System Software:
  10.16.4 10.16.4 (20E5210c) 
  Time since boot: About 6 hours

but then I realized that this build number 20E5210c appears to be associated with 11.3 BETA.

So you are running beta software. You need to use the feedback application associated with the beta program to report.

The rules of the forum forbid discussion of beta software.

But still you need to uninstall those antivirus, and turn on SIP.

Especially "cleanmymac", which is POISON to any sane mac.

Uninstall it completely, and never install any program that claims to clean, optimize or speed up your mac. They're scams and can cause crashes and issues, usually necessitating a full clean install of the OS the revert to sanity.

There is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This user tip describes what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community   

That being said uninstall CleanMyMac, Bitdefendeer and CleanMyDrive according to the developer's instructions.

When done you can check to see if you've removed all of the supporting files by downloading and running Find Any File to search for any files with the application's name  and the developer's name in the file name.  For the mentioned software you'd do the following search(es): 

1 - Name contains cleanmymac

2 - Name contains macpaw

3 - Name contains bitdefender

4 - Name contains cleanmydrive

Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.

FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  

Does it happen in all applications or just in Chrome?

Try switching to Light Mode, see how menus behave, then change to Dark Mode again.

Any difference?

If the issue persists, Please run Etrecheck and post its full report here. Use the "additional text" button and paste the report into the text box.

Oh, and consider ditching Chrome... it is very poor citizen of the macOS environment.

Please run Etrecheck and post its full report here. Use the "additional text" button and paste the report into the text box.

There may be something else involved.

Also: create a new user account, and test. Does it show the same problem?

Restart in Safe Mode. Does the problem still occur?

Also: to make a screenshot press command-shift-4 and drag.

If you take a screenshot of the whole screen with command-shift-3 the file may be too big to post here.

works fine on new account

EDIT: please ignore. The screenshot was not showing, but now it is.