Neither CSM nor WINDOWS 7 is an option with Latitude/INSPIRON 3580.
64 bit WINDOWS 10 is the only option for newer processors from now on.
Windows 7 is end of life in JAN 2020.
This is enforced by NVIDIA, ATI, INTEL, MICROSOFT, ETC.
Skylake systems were the last versions that supported windows 7 back in 2015.