I made sure to clean both sticks and CPU (even though it's brand new), nothing helped, tried literally everything, but finally realized it wasn't the board when I got the exact same issue on the Gigabyte Elite AX, refused to boot with a stick in A1 or A2, swapped CPU after I had cleaned the 12900K (when it still didn't want to work), and with the new CPU (12700K), instantly worked. But I'll keep that advice in mind.
Here's my first attempt at high frequency (back on the Strix A for now), only thing I did was set 133:100, 4133 MT/s, 16-16-16-28-2T, 360 RFC and 32000 REFI, 1.45V DRAM.
View attachment 2531638
I knew this specific overclock
should work since I ran the same but 280 RFC and 65K REFI 24/7 on Z370 Apex, I did try pushing it to 4266 after this screenshot but it was a no-go.
This specific memory kit is 2x 8GB Single Rank B-die from 2017, among the first ever batches of Trident Z RGB, highest frequency I ever booted with them on Apex was 4600, so they should do 4266 with some tweaking, but my first attempt at 4266 did not work, I will try and push it when I get some sleep, as well as push the 2x 16GB Dual Rank B-die from 2021 (December 2020).
(Also take into consideration that my 12900K was defective, meaning I have to use 12600K & 12700K which might mean the IMC is not as strong!)