The manual makes no mention of NVMe. However, with a modified BIOS (using UBU, UEFI BIOS Updater) and an M.2 adapter in the PCIe x1 slot, you can boot Windows 10/11. You must flash the NVMe driver into the BIOS.
This guide covers everything you need to know about the Lenovo IS6XM Rev 1.0 motherboard. Often found in ThinkCentre M91p Lenovo Is6xm Rev 1.0 Motherboard Manual
The 9-pin front panel header is . Using a standard PC case will require repinning. The manual makes no mention of NVMe
Locate the "CLR_CMOS" jumper near the battery. Move the cap for 10 seconds to reset BIOS settings. Fan Error: This guide covers everything you need to know
A: The TPM chip is soldered (discrete). Look for a rectangle near the SATA ports labeled "TPM." There is no external header.
Check the comments below, or head to the Lenovo Community Forums (ThinkCentre subforum) – many users still actively support the IS6XM platform.