Biggest issue facing mankind?

Over population. 

If you ask me, the biggest issue facing mankind as a whole is that we are using up the earth.  Everything on earth that we can dig up, tear out, cut down and sell, we're doing so without any thought of what we'll do when it's gone.  Capitalism, politics, and in many cases even religion are totally focused on the short term--the next election, the next war, the next stockholder's report.  Billionaires who make all the real decisions just want to make that next billion in the years they have left, and have no thought for what will happen after that.

So we're destroying wild habitat.  We're filling waterways and even the oceans with our trash.  We're overfishing our fisheries so there will be no more fish for future generations.  We're mining and grazing and timbering in our national parks.  We're destroying good farmland.  We're running low on clean water.  We're producing enormous quantities of trash and  hazardous waste with no idea how to deal with it.  All of these things are just seen as ways to make a few quick bucks in the short term.

I think the worst is global climate change.  Climatologists warned us about this 40 years ago and we are now seeing the very things they predicted, yet our government still can't admit it's even happening.  If you're young today, say below 30, this is going to affect your life enormously.  It's just easier for people to deny it than to worry about it.  Personally, I don't think we're going to do ANYTHING about global climate change until it's too late.  Half of politicians believe it's a hoax and the other half can really do no more than talk about it.  And we'll hear stronger and stronger denial even as it gets worse and worse.

Selfishness       

The widespread cancel culture largely perpetrated by the media. The proliferation of false news and information, again perpetrated by the media. Another problem is racism, not just from whites, but from all races.

Take those three things away, and we may very well have world peace. 

Other than the Covid pandemic?

I'd say the fact that we're all so spoilt nowadays. As someone born in 2000, I'm disappointed in my generation. But 2020's kids are surely going to be even more spoilt

The New World Order clamping down and tricking everyone into self quarantine.

This was only a test run to see how many idiots can be tricked into submission.

Overpopulation. Too many people are having  babies and filling their minds with lies and racist mentality. These people rarely seek employment.

Instead they collect their welfare money at the expense of others. 

If you are a bitter, angry, resentful person. Do the entire world a favor. 

Don't have any children until you seek professional help.

Making sure that food production continues.

God help us if the socialists seize the "means of production" and there are food riots.

religion is the cause of all problems. beggars and doormats are stuck in their old ways. and we're stuck with them