"The President decides..." within the limits of his constitutional powers. Which do not include, for example, impoundment or unilaterally shutting down agencies authorized by Congressional acts.
So, yes, impoundment is a relevant term to use.
To say nothing the freezes that have been put on hold by the courts.
If you think there’s a violation of the impoundment act, you need to identify what the “program” is and why you think the administration won’t spend the whole program amount within the relevant time period.