Gap in Flex.
Just like grid, gap works on Flex and columns too.
You can actually create a nice grid without even using CSS grid.
I you have an old site and you’re adding the gap using margin-bottom and margin right to create a nice grid. But you can just use gap instead. Keep in mind that some browsers still don’t support it completely.
Here’s one example of creating a grid view using flex and flex-gap. I have a fixed height and width set but you can always make the flex-items equal and leave those units set as 100%.