LrC Manual Export
Here are the steps for using Gigapixel as an external editor with manual export:
In Lightroom Classic, open Preferences and select the External Editing tab
Under Additional External Editor, select Choose and navigate to Gigapixel in your Applications folder
After selecting Gigapixel, close your Preferences
Right-click on your image, and hover over Edit In >
Select Edit in Topaz Gigapixel AI...
You will be prompted with options on how to send the image to Gigapixel
We recommend Edit a Copy with Lightroom Adjustments
This option passes your edits along as a duplicate file so that the original remains unharmed
After making your adjustments in Gigapixel, choose to Export image
On the right of the Export window, make sure Prefix and Suffix are empty
Disable Add applied filters to filename
Next, enable Allow overwriting?
Under Save to, select the option for Original Folder
These export settings will overwrite the duplicate created by Lightroom with the edited file coming from Gigapixel.