32GB (4X8GB) RAM Memory for Apple iMac 27-inch 2.7GHz Intel Core i5 | eBay
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Amazon.com: OWC 32GB (2 x 16GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S32P) : Everything Else
How to upgrade the RAM on the 27-Inch iMac (2020) | AppleInsider