Hello JBBlack,
I understand your concern buying DDR5 memory for your new system that is not listed in QVL.
And I agree with that when you are planning on buying pre-overclocked kits.
However the 4800MHz kits are basically default for Z690 chipset,.. so if the kit is not faulty they will boot into BIOS at 4000MHz.
Due to the fact they were not tested before release of your motherboard is generally why the 4800MHz kits are not all listed in QVL but all will default to 4000MHz.
Than you have the option to run ASUS Enhanced Memory Profile in BIOS.
The enhanced memory profile is optimized by Asus, so YMMV with the primary timings.
My Dell modules are listed in QVL on page 6,.. as SK Hynix, SK Hynix.

I have all three Dell memory upgrade kits listed, 2x8GB, 2x16GB, and 2x32GB kits. All three kits have different primary timings when running Asus Enhanced Profile.
The higher MHz profiles I listed above are the Pre-loaded SK Hynix profiles in BIOS, all are fully stable with current BIOS.
I bought my Dell memory upgrade kits direct from Dell back in November, they are currently sold out. Only place to buy today is on eBay.
When buying DDR5 memory on eBay you generally will pay double what Dell sells the kit for.
There are a few Dell kits currently listed on eBay, I would buy from seller with positive feedback, use PayPal.
$420.00 with free shipping:
https://www.ebay.com/itm/203795713080?_trkparms=amclksrc%3DITM%26aid%3D111001%26algo%3DREC.SEED%26ao...The Dell memory are bare modules, temps are fine without heatshields under daily usage.
I opted for installing FMMJ RAM jackets:
https://xtia.design/products/xtia-hao-fmmj-ddr4-ram-jacketThe Ram jacket system is a vary clean look to cover the green PCB bare modules.