I don't like the 'First world problem' retort, as, as has been said upthread, it is facile, and also because we live in the First world! If we didn't allow ourselves to feel upset/irritated by anything that didn't happen to people in the Second and Third worlds, we would either be very 'Zen', or our standards would slip very quickly.
I think that most 'think yourself lucky' comments are unhelpful, as if something is upsetting someone, it is upsetting them, and that's all there is to it. Knowing that others are worse off is not going to improve matters - if anything it could make people feel worse.
If a reader thinks that a problem is trivial, it's better, in my opinion, to just ignore it than to tell the poster that she is over-reacting, particularly if the rebuke drags in the pandemic. It's a bit tasteless to do that, I think.