What happens after an extensive volcanic eruption?
Lots and lots of ash thrown into the atmosphere.
When Mt St Helens erupted, day light turned to night light in the surrounding areas. The museum near Mt St Helens has great videos showing all the aftermaths from the eruption.
Ditto when Krakatoa erupted in SE Asia, the darkening effect lasted long time. Which then leads what would happen if a giant asteroid big enough to cause crater the size of Gulf of Mexico. Yeah a nuclear winter lasting months. Those large Dinosaurs were cold blooded animals like Crocs are. They become immobile with cold. They had no energy to hunt for food. Thus they may have just starved to death.
The small mammals of that era on the other hand were warm blooded animals and can regulate their body temp better and many survived. Try this experiment. Place a gecko lizard in a jar (those are ubiquitous here in Florida and they eat insects and have no teeth and are cute) and place the jar in your fridge. Then catch a mouse and do the same thing. The cold blooded gecko will lie immobile and asleep. The mouse will be awake and respond to opening the fridge. That is the difference between cold blooded and warm blooded animals.
It doesn’t take much to darken the skies. In 1991 gulf war, the oil well fires blocked the sun quite well. I saw it. So Ehat you say about volcanoes is plausible.