How Does High IV Affect the Theta of a Deep ITM Option?

High Implied Volatility (IV) has a minimal effect on the Theta of a deep ITM option. Since a deep ITM option has very little extrinsic value, its Theta is already close to zero.

Even a significant increase in IV will only marginally increase the small amount of extrinsic value, leading to only a slight, almost negligible increase in the magnitude of its Theta.