How important is memory compatibility if its not on a motherboards QVL list?

[Pretzel12345]

Hello,

I am wondering how important it is if a set of ram isn't on a motherboards QVL list and if it would still "work"?

To some degree I understand that its not always be all end all, but I upgraded from an intel CPU to a B550 Tomahawk and R7 3700x and my PC has been freezing randomly and I've done extensive troubleshooting to no avail.
 

1. Half, then full windows reinstall
2. AMD driver update

3.BIOS update

1. memory test
2. drive tests
3. latest gpu driver
4. SFC scan
5. stable temps (30-40 on idle, never above 60 on load)
6. Locked memory speed to 2800 mhz
7. tried single channel

Next step is to replace parts, and well, my RAM isnt on the QVL list. They're g.skill f4-2800c17d (cheaper end ram when i first built my PC with an i5 6600 5 years ago)

The ram works just fine, but if its not on the list could it be a cause to my freezing?

[JunkGonPC]

Try running the memory slower (lower xmp profile?) Could be timing.

I think i remeber this from an ltt video.. xmp profiles dont hold full timing profiles so part of the qvl process ensures bios' has profiles that match/work (on the verge of guessing)