MacOS creates swapfiles automatically as needed (in /var/vm). It will allocate a lot more space to swap than the size of RAM, if it determines that's useful.

It's actually a problem, if you're low on SSD space the filesystem can fill up with swapfiles while the system is still reasonably functional because the SSDs are fast enough. Then because of an APFS design fault, sometimes it isn't possible to delete any files to free up space. It says "out of disk space" when you try to delete a file.