This answered my question. I created a reddit community about printing3dpeople.I can't find any software that allows you to create and then print them. I'd love to know how those model you buy online and print are created.

Hi there,
For 3D printing, we need to patch the holes. But CC3+ models are not "watertight".
I do not know anyone who is 3D printing CC characters. But perhaps someone in the forum is doing such.
On october 2022, I posted this issue: https://www.reallusion.com/FeedBackTracker/Issue/3D-Printing-mesh-optimizer-for-printing-3D-characters *
Is there anyone in the Reallusion community who has successfully 3D printed a character created with CC3 or CC4?
If so, I would like you to put me in touch with him !
Thanks ;)

* Recall of my post on the FeedBack Tracker:
I can't manage to make a character compatible for 3D printing.
- Although I used the LOD functions by simplifying the mesh and merging the clothes with the character, the 3D printing software says that there are holes, making it impossible to print.
- I tried with the CellBlender add-on is a Mesh Analysis tool that allows you to check that the model is manifold and correct it if it is not. No way.
- I solicited a 3D printing expert who preferably uses "Netfabb" which solves a lot of problems.
He also tried to fix it with "3D builder" is also a good solution to automatically make STL files compliant for 3D printing.

But nothing worked !
The character file contains too many errors and too much repair work.

I thought that Reallusion had created a function that I would not have discovered in CC3 or CC4 to optimize the mesh for printing 3D characters.
Perhaps this function should be suggested to the dev team?

Hoping it helps,
Cheers,
PhiBix