Only certain mirrorless lenses ate compatible with teleconverters, and that one isn’t. Teleconverters are also surprisingly expensive. RF mount is also expensive because Canon banned third party lenses entirely until recently and continues to heavily restrict them.
While photographers use a variety of focal lengths for portraits, the focal length that’s most associated with portrait photography is 85mm. This article from lens review site Imaging Resource illustrates the point; most of the lenses are 85mm or equivalent (e.g. 42.5mm on m43 with a crop factor of 2 making the field of view equivalent to 85mm).