Chosen Solution
The original GPUs in these 2010 iMacs are known to fail. I’m fully expecting mine to fail eventually. Today I noticed that I get this blocky effect on mouse drags after the computer has been on for a full day. I also saw this today (see image). Are these signs of a GPU starting to fail?
You might be able to save it! I’m suspecting the GPU board overheating. Time to take the system apart to clean the dust buildup on the fans as well as clean off the old thermal paste and pads replacing them with better quality thermal paste and pads (not gapping paste). I would also get a good thermal monitoring and control app like TG Pro it will allow you to monitor your sensors and fans as well as boost the fans speeds when needed!
