Slow Mac? Could be a GPU (Video Card) Failing
Mac video problems are bad news for iMacs and Macbooks and could signal it’s end-of-life
Slow Macs that show distorted screens or fail to start properly are usually caused by a failing Video or Graphics Processing Unit (GPU)
If your device is under 5 years old, Apple may still carry parts and it can be fixed.
Over 5 years old and your only solution is second-hand parts that usually have no guarantees attached.
If you have Video issues and the Mac or Macbook is older than 5 years old, it may be time for a new one. Dodnt use second hand parts unless you can get hold of them cheaply from a reliable source.
Some Mac have been recalled with Video Issues in the past, check this link to see if your model is one of them.