If you don't have one, or your PC is a bit older, you can still find a great deal on a SATA SSD. These are slower than NVMe drives but they're still a huge improvement on a traditional hard drive.
an internal SATA SSD could make your PS4 or PS4 Pro ~30% faster. One of the best external hard drives will absolutely do the trick though, especially since there are now great SSD options ...