UE5 bricks my (brand spanking new) iMac.

Hi,

If your iMac has intel processor, following document could help your question.

https://support.apple.com/en-us/HT208544

From your sub text it seems you have a 2012 iMac which is quite old now (brand spanking new?) and you need to balance the cost of adding hardware to an old computer versus the benefit of buying a new iMac.