Correctly formatting automatic APA 7th edition style citations in Word
Instructions on building your own custom citation style can be found at this Microsoft webpage.  This instruction can be used to learn how to modify the current style, or use it as a template for a separate corrected style.

In the meantime, whilst working on the style, I found a workaround for the et al. inline citations in SuperUser.  You may manually edit incorrect inline citations by editing the field.  Doing this is still quicker than manually typing all citations and references as it only affects a few inline citations.

For example, with the inline citation used in the question


  (Okami, Olmstead, Abramson, &amp; Pendleton, 1998)


right click on the citation and select the "Edit Field" option.

The citation field for this example was:

CITATION Oka98 \l 2057

If you edit it to this:

CITATION Oka98 \n  \t  \l 2057  \f "Okami et al., "

It becomes:


  (Okami et al., 1998)


The following explains the switches used.

\n removes the author names

\t removes the title (to prevent it being displayed with the other bug)

\l is for the locale code

\f is for a prefix which in this case replaces the author names.