Following this course (Blender Character Creator for Video Games Design) baking objects with multiresolution modifier worked for me with blender 3.22 by adding the character / image textures “orc cav.png” and “orc norm.png” to the material of the high poly mesh too (not only the low poly material) and make the textures the active ones by selection.
otherwise there was this error shown: “you should have active texture to use multires baker”.
When i have done it, both objects (low poly and high poly) had the multires modifier on. The high poly with a higher subdivison level (for example 3) and the low poly with a lower subdivision level (for example 1).
Maybe it works, when only the high poly object (the source) has a multires modifier, but i did not test this case.
