iMac19,1 - How many sticks of RAM should I be using?

I have the 2019, 27" imac, Intel Core i9 and currently have 64gb of RAM installed (2x 32gb installed in slots 2 and 4). I read an article that stated if you're going to have 4 sticks of RAM installed, you better make sure your CPU supports quad channel. Otherwise, two of the sticks will be rendered useless. So given that my CPU is only duel channel, would installing two more sticks of RAM, in fact, be useless? But if the CPU can support up to 128gb of RAM, and installing another 2 sticks of 32gb be pointless (according to the article) how am I suppose to max out? I'm not aware of any 64gb RAM sticks. And would adding another 64gb of RAM even be helpful? I mostly use my iMac for video editing (DaVinci Resolve).

Hopefully someone can clarify due to the conflicting information. Thanks!