I have a Samsung 990 Evo Plus 4TB in the right hand slot if looking down from the front of the computer, not sure which number slot it is.  I was thinking of adding a heat sink to it.  So far, mine only stopped once during some heavy data transfer.  I just turned the computer off, and removed and re-seated the card, and it has been working ever since.  I've also been thinking about removing the small plastic Fan cowling located to the left of the big plastic cowling that covers the processor area.  I think this smaller fan cowling blocks some air flow right below it where these SSD slots are located.  I think the SSDs could benefit from some extra air flow as a result of removing this fan cowling.

@pcnetpro​ Thanks, pcnetpro, for a quick and useful response.  BTW, I'm reasonably sure that your samsung evo was in slot 2, because slot 1 is a dedicated boot drive. The same day I got a direct email from dellsupport, saying that my samsung pro could not go in slot 2 because ssd slot 2  "does not support an NVMe SSD such as the Samsung 990 Pro and is intended for SATA storage devices."  

I responded that this claim conflicts with Dell’s own documentation and the physical board design: • The May 26, 2026 Dell manual lists both M.2 slots as PCIe 4.0 NVMe. • The board silkscreen identifies Slot 2 as PCIe x4, not SATA. • There is no SATA routing to either M.2 slot on this board. • The BIOS exposes Slot 2 only as NVMe PCIe, with no SATA M.2 mode available.  I will report back when I get dellsupport's reply.

Again thanks, pcnetpro, your shared experience with your samsung card may have been crucial in dell support's resolution of this issue: "After re-engaging our next-level support team and reviewing the system configuration again, we would like to provide a correction to our previous communication. 
Based on the latest review, your system includes two M.2 slots that support NVMe SSDs. We have confirmed that M.2 Slot 2 can support an NVMe SSD such as the Samsung 990 Pro. Additionally, the installed NVIDIA RTX 5080 graphics card is connected through a separate PCIe slot and does not prevent the use of the second M.2 slot " 

Also, you mentioned that you were considering adding a heatsink to your samsung.  I suggest you choose a low profile heatsink (5-7 mm).  The EBT 2250 has a tight vertical clearance envelope around slot 2.