What are PCI Express 4x slots made for?

This is a 4x card and I know that most of the time this will work without issue But in my experience with Dell PE servers compatibility is a

I found things online like riser cards that seem to take one 16x lane and split them into 2 8x lanes, or 4 4x lanes, etc My thinking was if I

4x4 mega slot PCIe slot, with some computers having multiple PCI Express slots 4x, 8x, and 16x slot configurations, increasing the maximum potential

4x4 super slot Likewise, PCIe x16 refers to a Gen 4 expansion card or slot with a 16-lane configuration And so on Each new PCI Express generation doubles