This is the relevant screenshot from the Help documentation page that Daniel had linked above:
On the right side of the above image, it shows where the individual vault item’s behavior can be customized.
I also agree with the advice provided by Kent — instead of disabling Autofill for the problematic websites, a lot of times the problem can be solved by defining custom fields. Users on the Community Forum can often help, if there is a specific webpage that you need to configure.