Hello ,
Thank you for posting in the community about trying to use a Quixel surface with the substitution table. When trying this feature with the Quixel assets I ended finding an issue(crashing) when using the GUID from the quixel asset and have reported this to our development team.
However at this time you can still get the substitution to work for those assets but you will need to download the Quixel surfaces first, place those surfaces on an object then save that material in the user library. Once that is done you can open a new TM file and export a CSV file from the file menu > export all libraries.
You will be able to see listed in the CSV file the user library surfaces with the GUID information needed and replace it accordingly in the substitution table file.
Here is the location for the default substitution table file that you can edit and save a copy as needed.
C:\Users\USERNAME\Documents\Twinmotion2022.1\Substitution
Here is the link to the overview article on the substitution table:
https://twinmotionhelp.epicgames.com/s/article/Twinmotion-Substitution-Table-Overview
Hope this helps and let me know if you have any issues with this.
Kind regards,
Vincent B.