Serge B,
you can easily make an orthomosaic of a wall in the Pro version, so no need to do it in an external application.
Please have a look in the manual, page 47:
"Orthomosaic is a combined image created by seamless merging of the original images projected on the
object surface and transformed to the selected projection. A polygonal model (mesh) or a digital elevation
model can be selected as a surface where the images will be projected to.
Metashape allows using one of the following projection types: Geographic, Planar or Cylindrical. ...."
Best regards,
Kiesel