A tech stack including Microsoft Teams, Apple Safari, and WordPress - all in the same project - might have been a red flag not to work with that agency

Might? You used that word, And I don't think you know what means...

Isn’t that the ritual to summon the devil?

How can Teams and Safari be components (part of the tech stack) of a WordPress site?

I didn't mean the development tech stack, but rather the technology required or expected. WordPress was set as a web development tech stack, Safari is what they seem to test by default (and yes, that damn non-standard browser is still THE NEW INTERNET EXPLORER), and Teams and Skype the default communication tools.

WordPress is the red flag