Where is "attach" field type?

In custom field form, I was trying to add a custom field of attach type in a form but there was no “attach” in the list according to the picture below. The guide at https://erpnext.com/kb/customize/field-types states this but I don’t see it on my ERPNext. Is there something I missed? Also I tried the other way via Customize Form (it displays “attach” in the list) but when I clicked save, it showed error message saying “Field Type cannot be “Attach”. It should be one of “Button”, “Check”, “Code”,…”. Maybe it’s a bug?

Yeah this is quite easy again. Added in v5

Ok, thanks. Look forward to V5!