I have 4 dimms of Corsair Dominator Platinum ram 3600mhz. 2 16gb and 2 8gb chips. I was under the impression that all 4 chips could run dual channel regardless of size? I am using a Gigabyte Master x570 board and I have my dimms as 8 8 16 16 (A1 A2 B1 B2) but cpu-z shows slot 1 is 16gb dual, slot 2 is 8gb single, slot 3 is 16gb dual and 4 is 8gb single. I can't get all 4 to run dual... I had them every other 16 8 6 8.
First of all, "Dual Rank" is not the same as Dual Channel
On the bright side, it should be less difficult to get your two dual rank sticks plus two single rank sticks to run at high speeds than four dual rank sticks would be. Regardless, four sticks still puts a heavier load on the memory controller so you may need to set more voltage and/or less speed than the memory is rated for.
Mixing ram sizes you get flex mode, no way around that. You'll get the (A1/B1) as 8+8 in dual channel, with the remaining 8 from B1 as single channel.
You'll only get dual channel across both with 8/16/8/16 (A1/A2/B1/B2) since A2/B2 are the primary slots. Programs will use the channels progressively, not synchronous, they'll use the 16Gb dual first, then if needed will use the 8Gb dual. Works the same way as flex mode uses the 8+8 dual channel first, then the remaining 8Gb single channel if needed.
And with Ryzen, speeds matter per generation. 3 series Ryzen or prior do not like 4 dimms at all and depending on rank will determine max general speeds.
If using 5 series, that doesn't apply since Zen3 uses ram slightly differently with the architecture change and 2x dual rank 16Gb in dual channel gets better performance than 4x 8Gb
Yep, all Zen architecture allows asymmetric dual-channel (just like Intel's Flex Mode has since 2004 with i9xx chipsets for Pentium 4). That means at least part of OP's RAM has been running in dual-channel this whole time, and if they correctly put a 16 and an 8 into each channel as you said then everything should run in dual-channel.