I have a (2012, I think) Mac mini.
After between 20 minutes and an hour of use it freezes, then goes to a black screen. Occasionally the freeze is preceded by graphics corruption, such as coloured squares.
A year ago, when the issue started, it would work for 2-4 hours before the same freeze and refusal to boot, so this problem is gradually becoming worse.
Removing the power cord, plugging it back in and switching it back on does not make it work. If I wait for some minutes or hours, it will boot again.
This makes me suspect some form of thermal issue, rather than software.
Is this a common fault on Mac minis? Is it fixable?
Is there a way to diagnose it? (I'm a Linux software developer - I'm not generally familiar with macOS).