https://wccftech.com/2020-27-inch-imac/

Apple has announced updates to its 27-inch and 21-inch iMacs. The 27-inch iMac has been updated with 10th generation Intel processors, double memory capacity, next-generation AMD graphics, 1080p webcam, improved speakers, studio-quality mics, and faster SSD storage. The 21.5-inch iMac has also been updated with faster SSD storage, while the iMac Pro has been updated with 10th generation Intel Xeon processors.

Instead of a redesign with thinner bezels to make it look modern like the Pro Display XDR, Apple has kept the same old aging design for the iMac and simply updated the internals. As expected, only the 27-inch iMac has gotten the best treatment, while the cheaper 21.5-inch iMac has received the bare minimum updates.