Chiming in with some info after my own struggles, which I now have resolved.
I bought a factory seconds version of 13" laptop, with i7 1165G7 cpu. I had a 16Gb 2400MHz DDR4 SK Hynix ram module lying around, so I thought to use that when the laptop would arrive.
No boot with that, not in either slot, not after power resets nor mainboard reset. Just the DDR init ok orange blink in post-code, indicating ram failure.
I even bought a second memory from a local store, a no-name with speed 2666MHz, thinking the first memory was faulty. Same issues.
It was only after going in-store with the laptop to try different ram modules that a working one was found, a Samsung 8Gb 3200MHz module.
My take on this is, Framework mainboards seem to be picky about the speeds and timings, especially on the lower end in my case. It may not be worth the trouble to try lower than 3000MHz modules or modules from non-reputed manufacturers, especially if you don’t already have a working system in your hands.
I guess I was spoiled with good luck in desktop systems working with all kinds of mismatched memory! This is a minor minus to Framework as a platform, but I find this acceptable as this is only issue if one wants to source the parts oneself without using officially supported ones.