RAM upgrade in iMac 2020

Install memory in an iMac - Apple Support

Follow the instructions for your specific model Mac. I recommend avoiding amateur advice. I also recommend OWC: https://www.owc.com/solutions/memory. There are few competent vendors, and Crucial is certainly one of them, but OWC is the only one I have used and can personally recommend.

Whatever you do, avoid PC-centric vendors. Macs are intolerant of RAM that does not absolutely positively meet Apple's stringent requirements. PCs can adjust to "faster" or "slower" RAM leaving the user none the wiser. Macs do not have that ability.

Follow the instructions in Install memory in an iMac - Apple Support.

If it doesn't say you have to do something, you don't have to do it. Disregard the amateur advice; there is plenty of it out there.

It really DOES NOT matter which slots you use. I've owned 2 2020 27" iMacs since they were released in 2020 and upgraded both with OWC RAM, both have run perfectly for years now.

You will not NOTICE any difference in speed that is unless you are super human and can detect super minuscule differences. However it's your computer, do what you want.

That's the reason I advised following the instructions in Install memory in an iMac - Apple Support. Third time now.

It's INCREDIBLY simple, use the empty slots!!!!!!!!!!!!!!! It's just RAM, don't over think the process!

In addition to the Apple Support article for that year model.

Have a look at > https://eshop.macsales.com/installvideos/iMac-27-inch-5k-2020/?filter=memory

Be careful when revisiting 2020 threads here. Crucial is not offering RAM for 2020 iMacs today. From their RAM selector tool:

Allan Jones wrote:

Crucial is not offering RAM for 2020 iMacs today.

RAM for 2019 & 2020 iMac models is currently available from OWC.