Just in case you haven't heard, there is some height limitations when selecting an SSD if you plan to use both the primary 2280 slot and the secondary 2230 slot. This should only affect you if you plan to have more than 2tb in the primary slot, as most of those are single sided ssds (flash chips only on one side).
If you plan to use both slots, Framework recommends you only use a single sided 2280 ssd in the primary slot and the secondary m.2 2230 slot must be single sided no matter what as there isn't enough clearance below to allow for it.
You can technically use a dual sided 2280 ssd in the primary slot, however for this circumstance there is a maximum height clearance which will still fit.
Primary Storage M.2 2280 SSD with a bottom side height of 0.7mm combined with Secondary Storage M.2 2230 SSD with a top height of 1.5mm.
Or
Primary Storage M.2 2280 SSD with a bottom side height of 1.35mm, combined with Secondary Storage M.2 2230 SSD with a top height of 1.35mm or 1.2mm.
They mention that you shouldn't have an issue if you use the Western Digital 2280 ssd's they sell. It seems the 4TB WD SN850X, while dual sided, has the flash chips on the underside all the way at the end. Which should be past where the secondary ssd sits, but I can't guarantee that.
Full details in the link provided.