I've seen a few people describe these as unit-only missions certainly across Warcraft, C&C and games of that era. Here's a few references using the term for warcraft specifically.
 https://jdgamingblog.blogspot.com/2020/10/the-past-and-times-of-yore-warcraft.html

https://www.ign.com/wikis/warcraft-3/Chapter_3_-_Ravages_of_the_Plague

It's also used over the internet to describe the C&C 'Commando missions' (although "The commando missions" is much more common!), single-unit missions is also used,  (obviously for a sub-set of these!)

I've seen a few people describe these as unit-only missions, certainly across Warcraft, C&C, and games of that era. Here are a few references using the term for Warcraft specifically. 

The Past and Times of Yore: Warcraft, Orcs and Humans, where RTS all began. JD's Gaming Blog

I found myself looking forward to the unit-only missions where you didn't have to build and defend a base […]

Warcraft 3: Reforged Guide - Chapter 3 - Ravages of the Plague. IGN

This is another "unit only" mission, meaning you won't have to worry about building a town.

It's also used over the internet to describe the C&C 'Commando missions' (although "The commando missions" is much more common!), and "single-unit missions" is also used, (obviously for a sub-set of these!)