I googled this and got this answer, where it says it can be done in the UV editr.
I should select a different slot everytime I render. But where exactly do you I choose the slot? I don't see an option in the UV layout.
However, I was looking for something more like what I see in this other software.
My UV panel:
However, I was looking for something more like what I see in this other software.
oogonzales use the Image Editor:
The same options to choose your Slots are in the UV Editor.
If you want this 'split screen effect'. you need to Save your Renders as Images and then use the Compositor: