OPEN IN not showing anything

Actually, you have three options:

You can open a file into Topaz software from Bridge by right-clicking a file and selecting from here:

Alternatively, you can access Topaz's software as a Photoshop & Lightroom Classic plugin. So, to use Topaz software, open the file in PS and then select the Topaz plugin from the Plugin menu.

With LR Classic, you have two options: You can open the image into Topaz directly as a raw image from File (menu) -> Plugin-extras. The negative is that you'll see the file before ANY of the LRC operations have been performed (no cropping, adjustments, or Masking). Otherwise, you can open an image in the Develop tab in the Photo (menu) -> Edit in …. Here, you will be given a choice to open the original or a copy with LRC adjustments. In this case, it will open as a TIF image. When you close either LRC version, the newer image (unless you open the original file) will become a Stack of the original image. 

Good luck!