Yes, you can
Jeremy Crawford confirms this on Twitter.
@JeremyECrawford After Haste ends, PHB says target can't move or take actions. Does this include reactions? Advantage to hit target?
Actions and reactions are different. If an effect, like the haste spell, shuts off one, it doesn't necessarily shut off the other. #DnD
Other supporting evidence
In the PHB, the Incapacitated condition differentiates between actions and reactions:
Incapacitated, PHB 290
An incapacitated creature can't take actions or reactions.
Actions and reactions are different.
If you had haste and fly on (concentration can be dealt with via potion, buff from ally, magic item, etc), and someone cast a dispel magic on you, you can still catch yourself with a feather fall.
If you were frozen with lethargy, you can still muster the "energy" to cast shield, hellish rebuke, absorb elements, or even counterspell, and perhaps you can narrate it as one desperate wave of the hand and a breathless incantation.
Ending haste does not incapacitate you. It just makes you lethargic and unable to take actions.