[NAME]​   LONG answer with solution at the end.    Even the Windows 11 install media can't see the SSD.  So I put a bullet in the chamber (so to speak) and switched the BIOS from RAID to something I've not seen before ACHI/NVME.  I've seen ACHI before but not PAIRED with NVME.  Now the Windows 11 media AND my recovery media see the Dell supplied SSD and it's being backed up.  Of course Win11 crashes on boot now because it only had RAID drivers installed.    NOW I REMEMBER - I've even written a post about this before.  I need to buy new Dell's EVERY year so I don't forget this trick.  SOME, maybe not all Dell systems come with the SSD/HD configured for Raid in the BIOS.  Most native media (Windows 11 installer and some recovery media) will not recognize these drives.    ANSWER:  For Win11 and likely prior, to get past the OS crash on boot when switching to ACHI/NVME...  1. RAID mode active and Win11 running - boot into Safe mode.   2. BEFORE the OS boots however, go into the BIOS - F2 - and switch to ACHI/NVME. 3. NOW boot and let Safe mode come up - Google Safe mode for details but you want to select Safe Mode With Networking. 4. Let it run for a few minutes  I'd had to do this LONG ago with another Dell.  I'm not 100% sure if networking is required, but with this method the OS is able to boot then magically installs the necessary drivers that allow you to use ACHI/NVME going forward.  Beats having to hunt down the drivers and manually install them. 
So, legacy boot is no more.  Testing out an 8960 and trying to figure out how to backup the single boot drive via off-line media - i.e. Acronis.  I usually do this on new machines and twice/year on in-service machines.    My USB recovery media is configured for UEFI and boots fine.  However, the recovery media can't see the system disk at all though.  I've not checked but I'm assuming bitlocker is not enabled by default.  
XPS 8960 USB boot - for offline backup