Are Ghouls and Ghasts vulnerable/sensitive to or affected by sunlight at all?
It says nothing in the Monster Manual, but they are undead, and I seem to recall that being a thing in previous editions.
Nothing in the monster entries for ghouls or ghasts mentions any kind of sensitivity or vulnerability to sunlight, and there are no universally applicable rules which would imply as much. We only note that "ghouls roam the night in packs", from which we can infer that these kinds of creatures are primarily nocturnal - which would make sense for a creature which can see in the dark, giving it an advantage over most of its humanoid prey.
Many magical effects which are thematically based on sunlight - such as the spell Sunbeam - are especially effective against undead creatures, so you could construe that as a kind of vulnerability to sunlight which is shared amongst all undead. Ordinarily, though, ghouls/ghasts are not hindered by lighting of any kind.
As you later recalled, ghouls are put at a mechanical disadvantage by light in the rules of Chainmail - where Wights (and Ghouls) subtract 1 from all die rolls while in "full light". This weakness is however not mentioned in OD&D's Book II: Monsters & Treasure, and doesn't seem to have resurfaced since - there's no mention of such a weakness in the 1e AD&D Monster Manual entries for them, nor the 3.5e ghoul/ghast entry (or the general undead traits in that edition).