I don't mean other people's suffering in the sense that atheists were indifferent to the suffering of others. Rather I mean, is the suffering in itself — their own and that of others — without meaning or goal, from the point of view of atheists (or agnostics)?
Yes, suffering exists. It has no intentional, objective meaning. Life is not fair. It’s how you take it and what you make of it. You can either let it crush you, or do something about it if you can, and if you can’t just accept it with equanimity and move on and not let it get you stuck. I like the approach of the ancient stoic philosophers.
"Make the best use of what is in your power, and take the rest as it happens. Some things are up to us and some things are not up to us. Our opinions are up to us, and our impulses, desires, aversions—in short, whatever is our own doing. Our bodies are not up to us, nor are our possessions, our reputations, or our public offices, or, that is, whatever is not our own doing."
-Epictetus
Incidentally, their philosophy was later adapted by Christians, but it works just as well with or without a god:
“God, grant me the serenity to accept the things I cannot change,
the courage to change the things I can,
and the wisdom to know the difference.”