We’re a Mac house at Purple so this comes in at number 2, even if it’s not applicable to everyone.
SATA drives are mechanical with high speed spinning parts inside. They are high capacity. Flash or solid-state drives (SSDs) have no moving parts and are smaller capacity for the same money. Both have advantages but SSDs are 10 to 20 times faster than SATA and tend to fail less often as there is no mechanical wear. Fusion or hybrid is a blend of both.
As recently as 2020, Apple were still selling new iMacs with SATA drives in them, despite the whole operating system being highly complex and practically designed to run on SSDs. New iMacs running the latest operating system, out of the box, were running horribly slow.
If you have a Mac or PC, check out the disk type. For Macs, Apple menu > About this Mac > Storage and check the label under the grey hard disk icon. Anything other than Flash or Solid State is very likely to be the root of your performance issues and you should consider an upgrade. For PCs, press Windows + R to open the Run box, type dfrgui and press Enter or Return. The disk type will be shown.
Don’t forget that a hard disk can also fail. This can definitely make a Mac running slowly. SATA drives become more and more likely to stop working every year after their third birthday. The not-so-sweet spot is usually around 6 to 7 years. A gradual but rapidly worsening performance problem with your computer is usually a sign of an impending drive failure.