If you are able to launch DeNoise AI as a standalone but you cannot launch as a plugin from Photoshop there are a few things you can do.
Note: this is very common in Photoshop 2020
1. Hold down CMD + SHIFT + G to open the Go to panel.
2. Paste in the path: /Applications/Topaz Labs LLC/Topaz DeNoise AI/Topaz DeNoise AI.app/Contents/Resources/PS_Plugins
Next, click the blue "Go" button to go to that folder
You should see the DeNoise AI .plugin file, it should look something like this:
/Applications/Topaz Labs LLC/Topaz DeNoise AI/Topaz DeNoise AI.app/Contents/Resources/PS_Plugins
If you are not able to get here, something else failed, follow these next steps.
Go to /Applications/Topaz Labs LLC/Topaz DeNoise AI/
Right-Click or Cntrl + click Topaz DeNoise AI and select "Show Package Contents" to get inside of the app bundle.
Go inside the Contents Folder:
Go inside the Resources folder:
Go inside the PS_Plugins folder
And your plugin file will be there:
This folder is always there. If you are not able to get to this folder go to the beginning of the article and make sure you are following the directions. If you open a help center ticket because you cannot get to this step, please include screenshots so we can figure out why you are unable to get to this folder and give you further direction.
3. Open a new Finder window using CMD +N. You should now have two Finder windows open.
4. Hold down CMD + SHIFT + G to open the Go to Panel in the second Finder window.
5. Paste the path: /Library/Application Support/Adobe/Plug-Ins/CC and hit the Go button.
It should look like this:
See the two screenshots below. Your DeNoise AI installation plugin folder is in the top Finder window, and the Photoshop CC folder is in the bottom Finder window.
6. Drag and drop a copy of the DeNoise AI .plugin file into the CC folder. Your computer may ask you for permission to create an alias. That is just asking for permission to create a link pointing back to the DeNoise AI plugin file. Enter your password so that the computer can do this.
Enter your password when it asks you to and it should look like this after you have done the drag and drop to create the alias pointing back to the DeNoise AI plugin file:
7. Open Photoshop again
8. Right-click on your background layer and select "Duplicate" to make a new layer that is not locked. (Plugins cannot be launched on a Locked layer)
Make sure the unlocked layer is selected.
9. Select Filter -> Topaz Labs -> DeNoise AI to launch your plugin