Backup of foul smelling water into the dishwasher

Outlet pipe is partially or completely blocked.

Use a dishwasher cleaner in it, but before you even do that, remove outlet pipe from waste pipe - and clear all the gunk out you can.

I suggest a bucket with disinfectant and washing powder to dissolve the grease.

You may need a drain cleaner down the waste pipe too - & flush with hot water and washing powder.