Question about Canon EF 1.4x III

Not combatable according to canon

I do not know the lens.
With my EF 100-400 1:45. -5-6 L IS, this converter only works in manual mode (i.e. no autofocus).

Unfortunately, this is not possible for several reasons.
See also :
https://www.the-digital-picture.com/Reviews...
https://shuttermuse.com/canon-came...

At 50mm the two lenses touch!!! And you don't want that ...
Even if the lens should work there is still the f8 problem (aperture extension because of extender). Only a handful of cameras can still focus automatically at f8. All other models have to focus manually. In the past, this was easy with the right viewfinder (sectional image with 2 semicircles.) Unfortunately, this type of viewfinder screen no longer works with modern cameras.