Thats why they release RF converters tooI'm starting to suspect the "unheard of!!!!" part of that macro lens is that it won't do macro
It may be imposible make 100-400mm 1:2 without focus breathing so they made 100-500mm . Without 1:2 even canon cant name it macro.
100-500mm 1:2 macro is just on verge what can be done with new 2 focus motor tech !