Sorry for the ignorant question, but with i7, 32GB, 1TB SSD, why isn’t this compatible with Win11?
This unit has 6th generation Intel processor.
Windows 11 requires 8th generation Intel processor.
Other than the Windows 11 thing, it looks to be a pretty solid machine for the price …
Any problem converting this to Linux?
I don’t foresee any issues, as the platform has been certified by Red Hat at the enterprise level:
Earlier versions of Ubuntu was even officially supported by Dell:
https://www.dell.com/support/home/en-us/drivers/supportedos/precision-t3420-workstation
(Note that I am not staff. I just volunteer to help out on the forums.)
Win 11 installs on most anything. You just need to use the ISO and the USB to install from scratch. Windows updates still work too. Also for Dell they have drivers. Download Dell Command Update.
Windows 11 requires a special TPM chip(encryption). Windows 10 has only 2-3 years left. Maybe like XP and Windows 7 it will last longer. I would not spend money on a machine running Windows 10. Check the Internet about when W10 dies.
FWIW, these do have the option for TPM 2.0 – which is a Windows 11 requirement – along with being capable of secure boot. A couple of the CAD workstations I deal with at work were equipped as such; however, Microsoft’s CPU cutoff still applies.
Since W10 support doesn’t end until October 2025 and these still handle our workload just fine, I haven’t proposed any replacements yet.
Maybe I’ll just push everyone over to Linux. 
(Note that I am not staff. I just volunteer to help out on the forums.)