Meshroom is great, but its output has two problems:

The UV maps it creates pretty much suck.
Accompanying the geometry of your object will be a lot of junk geometry.

To address this you need to interrupt the node flow, edit the outcomes in an external app, then pipe the result back into Meshroom. This process is described in the Sketchfab link (section: Retexturing after Retopology) and also in the manual. In brief, the process is:

Allow the Meshroom process to run up to the MeshFiltering node.
Right click on the MeshFiltering node and select Open Folder. This will open the related folder in the Meshroom cache.
In the MeshFiltering folder, open the model and edit to your heart's content. Mostly your task will be to delete the junk geometry, and remake the UV map. However, whatever you do, don't change the size or position of the model. Save as an obj. You may do this in Blender, but it is faster in MeshLab which is open source software for editing and analyzing triangular meshes. However, MeshLab's interface was designed by sadists who live in dark tunnels deep within the earth.
Remove the Input Mesh connection of the Texturing node (right click, remove).
In the Other Input mesh parameter of the Texturing node, write in the path of your new model. This will force the Texture node to process your new model and its new UV map.
Re-start the Meshroom process from the Texturing node. This will project the texture onto the new mesh and UV map.

Following this, you will now have a highly detailed mesh with a decent UV map and a texture. However, you still have a way to go.