That case involved two school nurses fired alleged for advocating for the rights of their disabled students. It's not difficult, however, to see how this holding translates to a situation involving, for example, COVID accommodations for employees
Imagine, for example, a supervisor or manager advocating for an employee at high risk for COVID-19 complications to work from home as a reasonable accommodation exception to the company's return-to-work program. Or HR advocating for an exception to a mask policy for an employee with pulmonary disease. Or someone advocating for a co-worker to have a flexible work arrangement because of childcare-related concerns.
This advocacy for others absolutely qualifies as protected activity under the ADA, and to react adversely because of it will result in a retaliation claim that will be difficult to defend. Embrace employees who have the empathy to advocate for their disabled co-workers; don't retaliate.
* Photo by Gabrielle Henderson on Unsplash