I have been seeing this on various sites regarding three days of darkness in the latter days which would occur as a means of chastisement for those living on the earth. From the Catholic perspective, Marie Julie Jahenny and Padre Pio have spoken about this, especially due to the moral decline of the priesthood.
It has also gained traction among Evangelicals who perceive their role as watchmen.

Any Catholics or others have perspectives on this?

There have been quite a few that have predicted it or say they have been told by Mary. I could easily see it happening, but no way to know for sure. It will either happen or it won't. I personally love the idea of obvious signs coming our way, but i stay hesitant to rest my faith upon private revelation.

St. Louis de Montefort and Bartholomew Holzhauser had some interesting predictions (maybe prophecy?) as well. They didn't call for the 3 days of darkness, but they did say that there would be world wide chaos followed by a period of true world peace before the end times. Mary has also alluded to a peace that will be coming after **** hits the fan. That's where my hope is now.

There is definitely a lot of stuff being discussed about a great enlightenment of conscience where God is going to essentially stop the world and reveal to all people the state of their souls if they were to die at that moment. Look for stuff from Father Rodrigue on YouTube. There's quite a bit of stuff out there on this.

Here are a few, there are many others:

Dr. Tylor Marshall made so good videos on this. Several saints have suggested there would be one, Padre Pio was not one of them. It is private revelation so Catholics aren't obligated to believe it, but there is not anything contrary to the faith within it.

I like Marshall's take of "maybe, maybe not. But I'll have some blessed candles around just in case."

I thought Padre Pio had endorsed the idea.

If you start at 4:54 there is a re-reading of a letter he is supposed to have written.

Me too, and a Purple Scapular.

I have seen that before, but not everyone one supports he wrote that letter. Since there are a lot of other saints and venerable people that have written about it I don't know if it is necessary to attribute anything to St. Pio. I think because of the stigmata and being a mystic it is plausible that he could have said something but isn't certain that he did. My rule if thumb on private revelations and Marian apparitions is to go with the ones the Church has approved.

Ah, I understand now. So the authenticity of the letter itself was in question, then.

A couple of Canadian Bishops have disavowed Fr. Rodrigue.

Loosely based on Jesus saying the only sign given will be the sign of Jonah in the whale for three days and nights.

The sign of Jonah was His death and resurrection....?

Telling you what its based on, the follow up argument to your question would be layers upon layers, precepts upon precepts. Or something like that.