Use Size Type - Mercator Sizes or Fixed Sizes to still be able to combining them accurately.

Or you can try the following:
Generate your area with the minimum settings you can set, with no textures or additional elements.
After generation, split the objects into scenes, and re-generate them in good quality.
I have no idea if this will work for 10000 tiles.
That's the highest value I've heard among everyone who wrote to support.
But this is the only way to generate the whole area that might work.

API:
https://infinity-code.com/doxygen/real-world-terrain/
Example:
https://forum.infinity-code.com/viewtopic.php?id=1447

Unfortunately it is not possible out of the box.
RWT works in such a way that it first creates all terrains, then generates heightmaps for all, then textures for all, then other data.
This is done to optimize performance and memory usage.

You need to split your generation process into multiple starts either manually or using the API.

since this process for RWT is heavy and I sometimes experience crashes I would like to know if is possible to disable the tiles after they are created and unload them from the scene.

I'm open to any suggestion to deal with it