Embarrassingly, it’s not possible with the built-in macOS Time Machine backup scheduler to only automatically create backups when the computer is inactive/idle. Further, Time Machine is apparently neither very efficient nor resource friendly. I’ve experienced many times that the automatic backup process kicked-in during a Facetime or Zoom call, severely impacting the call experience.
Luckily, the following 3rd party Time Machine scheduler solves the problem: TimeMachineEditor