The Feeblemind spell provides a list of things that can end the spell, but it may or may not be exhaustive.
Can the effects of the spell be ended by the Paladin's Cleansing Touch feature or the Arcana Cleric's Spell Breaker feature?
The Feeblemind spell provides a list of things that can end the spell, but it may or may not be exhaustive.
Can the effects of the spell be ended by the Paladin's Cleansing Touch feature or the Arcana Cleric's Spell Breaker feature?
The duration of feeblemind is instantaneous. So the spell itself ends as soon as it is cast. The effects of the spell endure after the spell itself.
Cleansing Touch ends a spell, not the effects of a spell. As such, Cleansing Touch cannot end the effects of feeblemind.
The relevant passage from the Spell Breaker class feature of the Arcana Domain cleric (SCAG, p. 126) is:
... you can also end one spell of your choice on that creature.
Since feeblemind ends instantaneously, there is not an ongoing spell for Spell Breaker to end. The ongoing effect of the spell does not mean that the spell is on going.