I do nothing.
I just sit there and listen to them, curse with them and let them blow as much steam as they need, you’d be surprised but most of the time people already know what to do, all they need is to be allowed to embrace whatever they are feeling at the time, to be heard and some empathy.
If you are afraid of an awkward silence then don’t be, sometimes just sitting in silence with someone can go a long way. Sometimes just little questions about it can help them open and show that you care.

Not everyone wants help, not everything has a fix, not everything has to be fixed on the spot, forcing someone will only make them double-down or close themselves and that can get worse because they’ll stop looking for help.

Obviously… this is in general what I used to do, everyone is different so each person requires a different approach,

You’ll have to be more specific with your question because… if I’m pointing out a toxic positivity attitude and you tell me you don’t know what a more desirable reaction would be, it concerns me… a lot.

Time to get downvoted for having an opinion, here I go:

In my experience, women were the ones constantly telling me I should be positive, I should smile/laugh more, I should not worry or cry or stuff like that (even lovingly telling me to shush), male friends were MUCH more accepting when it came to my emotional problems (both were equally useless tho).
BUT I don’t blame women nor the patriarchy, I blame toxic positivity, as most of us weren’t taught how to deal with emotions and came from toxic/broken homes so forcing a positive take on everything and shunning anything that could weaken that bubble was (and still is) the norm and that is genderless, assholery is a human thing, not a male vs female thing.