Optiplex 7090 Nvme PCI 4.0 Gen 4 support

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@dcol , please forgive me if I don't understand your issue as English is not my native language.  But the owner manual shows the specification for your system with Intel chipset Q570 and the PCIe bus support up to Gen 3.  The storage specification also show PCIe Gen 3 as well.  

Did you configure your system with a Dell gen 4 SSD, class 40?  If you did, then Dell must have given you a wrong motherboard option.  Some of their models can't be upgrade or add-on post sale.  Some customer ordered without discrete graphic and wanting to add later just to find out the motherboard only has soldering marks but no PCIe slot.  Whatever the case, I wish you the best outcome.

Now look at the newest specs which does show support for GEN 4

https://www.delltechnologies.com/asset/en-us/products/desktops-and-all-in-ones/technical-support/optiplex-7090-towers-spec-sheet.pdf

This must be a BIOS limitation because the hardware supports GEN 4

I want everyone to know not to expect this model to support the Dell Samsung PM9A1 or 980 PRO in GEN 4 Transfer mode. I assume the PCIe slot also does not support GEN 4. Very mis-leading.

Optiplex 7090 Nvme PCI 4.0 Gen 4 support

The Optiplex 7090 Tower specs says it has support for PCIe 4.0 GEN 4. I am using an 11th Gen i9-11900k processor. The Nvme slot 1 does not seem to support my Samsung 980 Pro PCIe SSD as GEN 4, only GEN 3. The specs also show GEN 4 compatibility with 2TB GEN 4 Nvme M.2, but it is only giving me Gen 3. Is this a BIOS issue? I am running the latest BIOS. Support would not help me or answer any questions since this is not a Dell part.

pcie 4.0 nvme requires a 12th gen processor. Even with that said the 7090 does not support it which is why I returned mine and ended up building a custom pc

Yes I know the chipset supports it, so there must be a BIOS limitation because the best you can get with the 7090 Tower is NVMe Gen3. The response from Samsung Magician is the motherboard does not support Gen4. That is why I returned my 7090 Tower.

For 7090 Tower - PCIe from Nvme 1 slot is plugged directly into CPU which does support PCIe Gen4 (CPU has 20 PCIe lanes, 16x for GPU and 4x for Storage) if you're using i5/i7/i9 versions of 11th Gen CPU (which you do)

7090 SFF doesn't have Nvme slot1 implemented (there's placeholder where socket is not soldered in).
It has only second Nvme slot soldered in.

Q570 chipset doesn't support PCIe Gen4, it works on Gen3 standard
(and some lower versions for compatibility)
This is the reason second Nvme slot supports only up to Gen3 of PCIe
(since it's plugged into PCH/chipset, not CPU)
CPU works with chipset / PCH via DMI bridge (combined bandwidth: 8Gb/s, for all devices together).

So your statement about 11th gen CPU not supporting Gen4 PCIe is not entirely correct.

Second problem might be with Samsung 980 Pro - it's implementation of PCIe Gen4 is via their own controller supporting only 1.3 version of PCIe Gen4 standard while popular Phison e18 works on 1.4 specification standard. Therefore Samsung drive is missing function of access to Host RAM and works by loading CPU too much, so expected to be slower on many workloads relying on this functionality.

Depending on type of work you do there might be drawbacks from switching to 12th gen CPUs platform since on most motherboards support for AVX-512 instruction set on 12th gen CPUs would be disabled (hence slight productivity drop under some specific workloads).
But as trade-off - yes, it's generally worth making a switch to newer platform due to other advantages (core count and efficiency, native Gen4 PCIe, etc.)