A triggered ability may have an instruction followed by “Do this only once each turn.” This ability triggers only if its source’s controller has not yet taken the indicated action that turn.
July 23, 2021 · Adventures in the Forgotten Realms
An ability triggers only if its trigger event actually occurs. An event that’s prevented or replaced won’t trigger anything.
June 18, 2021 · Modern Horizons 2
A triggered ability may have an instruction followed by “Do this only once each turn.” This ability triggers only if its source’s controller has not yet taken the indicated action that turn.