Why does Facetime echo and Zoom does not?

Huge echo with my living room setup when using Facetime on a Mac Mini with external camera (nice Logitech). Zero echo using Zoom. Or really, anything else. Even Skype seems fine. The echo is heard by the party being called, but not on our end. The microphone is on the logitech camera (C910, and BRIO, both attempted), the speaker is out of the TV. I have attempted to move both, turn down the TV volume, change positioning in the room, etc... Of course, it is convenient to use Facetime, but actually my mother and father are using this as the seed of a 'let's buy Samsung phones' plan. They hear good things. They switch, I'll likely need to switch.