EOS 90D & Rebel T7 won't go below F9 with 100-400mm & 2x extender III

[Drwho1300]

Using a 100-400mm in combination with 2x extender III on Rebel T7 or 90D. Once the extender is installed I cannot drop below F9 but AF won't work past F8. Any suggestions?

[ebiggs1]

As with most things in photography there is no right or wrong just what you are good with. There are some things I am unwilling to do or use and a 2x tel-con is one no matter the processing ability of editors.