Adding memory cards to 2020 iMac Retina 5K, 27"

Mac are very picky.

Your best bet is to order,

the 16GB 2x8 or 32GB 2x16 kit from OWC

https://eshop.macsales.com/shop/memory/imac-2019-27-inch

or the 16GB 2x8 or 32GB 2x16 kit from Crucial

https://www.crucial.com/compatible-upgrade-for/apple/imac-(retina-5k--27-inch--2020)-imac20-1

and then add those to the existing 2 modules.

Install memory in an iMac - Apple Support

Adding RAM will not speed up your computer, if that I what you are trying to do please do the following:

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community

We need to see your report in order to assist, as mentioned there is no personal information on the report and it takes multiple sets of eyes to see it as you can easily miss critical information. Please post per the instructions.

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