gaming on an iMac

I see this question quite frequently and I wonder why someone thinks that playing a game might damage a computer when often times watching video, working with photo filters, or even just browsing on the Internet can be more resource intensive than a game. Play games; have fun.

That said, babowa is right, the Mac has never been a popular gaming platform, especially for graphic intense 3D games at least. My wife is an avid Diablo III fan, I'm less interested in it. She plays on her MBP (don't ask me how she can play on a trackpad) and is quite happy with the performance. When I play it I do so on a PS4 and the animations are much smoother and the graphics more detailed.

Probably not, but Macs have never been considered "gaming" machines; the hardware/processor/graphics may not be optimized for it. So, it may not "damage" it, but you may not be happy with the performance and trying to play a game may slow it. Depends on the requirements of whatever game you want to play.

you can only run games made for macs though

steam has some, apples mac app store also have some

if apple made computer which would run software which would toll the system so much it would damage it, they would face a class action lawsuit in a heartbeat

The gaming issue is heat. I've done beta testing of games and sims on Macs and the current iMacs will get hot when running those with very detailed 3D graphics. The temps tend to get into the 140°F/60°C range before the built-in thermal system ramps up the fan speed to compensate (iMacs mades since late 2012 have only one fan). IMHO, that is a bit high before cooling relief comes.

Normally I don't like third-party utilities but I use a fan control app to manually set the fan speed higher before I start testing. There are fan utilities in the App Store.

In spite of using my iMac like this, I feel that iMacs are somewhat "under-cooled" for gaming. That comes from a"make it super-thin" mindset. That does not leave a lot of room for fans and air channels.

I'd like to see Apple reprogram the thermal system to react more quickly to temp changes, ramping up the fans at a lower temp that what I currently see. That would make iMacs better gaming platforms by reducing the harmful factor--heat, and eliminating the need for third-party fan control apps.

My iMac is close to top-of spec: 2017 iMac 5K 27" 4.2Ghz quad-core i7; 1TB Apple SSD; 16 GB RAM; Radeon Pro 575 4GB VRAM. There was an 8GB VRAM option when I bought it but I wanted to put that money towards the SSD. Games run very well at these equipment levels.

NOTE: Many high-end games require discrete graphics; entry-level iMac s won't have that. To get such graphics capability you need to get the 21.5-inch 4K model or a 27-inch.