Dual Channel Memory issues with Z790 Steel Legend

If you have both RAM modules in the A slots then you are not running in dual channel.
A and B indicate the channels, if you have RAM in A1 and B1 or A2 and B2 then you
are running in dual channel. 2 RAM modules installed does not mean you are running
in dual channel, they must be in the correct slots:

A2 and B2 (recommended) -> Dual channel
A1 and B1 => Dual channel
A1 and B2 => Single channel
A2 and B1 -> Single channel
A1 and A2 -> Single channel
B1 and B2 -> Single channel

The confusion is caused by how DDR5 works. As far as I understand it, DDR5 modules
function as if they are 2 modules in one (ie, Dual channel). If the information
I have been looking at is correct that means that dual channel is actually quad
channel with DDR5. This is irrelevant when it comes to performance however because
regardless of it being "dual channel" you are still losing half your bandwidth
with both modules in the A channel. Once 3rd party monitoring apps are updated
for the new standard properly it will stop being reported as dual channel with
a single module or both modules in a single channel.

The TLDR is that you should return your CPU if you are unable to get the RAM
to work properly in slots A2 and B2 or A1 and B1. That is a strong indication of
a weak or even bad memory controller on the CPU.

I hope this makes sense.