Hello, It is possible to replace the card with one of DELL MXM cards. For a 27”, the best choice is the Quadro K2100m as it runs cooler than the Radeon 6970m with a lower TDP and equal performance. Out of the box, you will get to macOS. But you will loose the bootscreen (can’t use the boot menu using the option key or access the recovery OS), no backlight controls and no target display mode. However, there is good progress made on this. This thread cover this well.https://forums.macrumors.com/threads/201...-imac-graphics-card-upgrade.1596614/ I upgraded my iMac and running Catalina as the Quadro supports Metal. Quite happy so far. As Dan mentioned, particularly in an iMac, dust and heat are the reason why the video cards are dying. I disagree that they are not designed to run intensive tasks. A GPU is design to run at 100% of its capacity when needed, especially without any overclocking, if it’s cooled properly. These machines were marketed by Apple for creative work not for word processing. The issue with...