US President Donald Trump's team has ordered the termination of vital support for F-16 fighter jet jamming equipment that Ukraine has. What is important to understand is that this could deprive the Ukrainian Air Force of its most important air countermeasures.
There is an aftermarket for F-16 planes and their spare parts.
Also, I should note that Iran (of all countries) is still flying its F-14 Tomcats, unless I’m mistaken.
The most immediate effect is ceasing updates for then AN/ALQ-131 countermeasures pod. If Russians come with a new radar or make their existing weapons behave differently, this could have considerable effect on the survivability of an F-16 in a hot situation.