I have one Lenovo ThinkCentre desktop M910 and one M710 with Debian 10 installed on both (now wiped out on M910).
I tried to install Debian 12 on the M910 but although the netinst proceeded without a hitch with GRUB installed on sda, it does not boot although it is accessible in recovery mode.
In the log, I got a red message saying that I would improve performance with a 64 bit install but I cannot find any 64 bit for Intel.

Below is the result of lscpu on the M710, I suspect the result will be very similar on the M910.

$ lscpu
Architecture: i686
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
Address sizes: 39 bits physical, 48 bits virtual
CPU(s): 4
On-line CPU(s) list: 0-3
Thread(s) per core: 1
Core(s) per socket: 4
Socket(s): 1
Vendor ID: GenuineIntel
CPU family: 6
Model: 94
Model name: Intel(R) Core(TM) i5-6400 CPU @ 2.70GHz
Stepping: 3
CPU MHz: 905.032
CPU max MHz: 3300.0000
CPU min MHz: 800.0000
BogoMIPS: 5399.81
L1d cache: 128 KiB
L1i cache: 128 KiB
L2 cache: 1 MiB
L3 cache: 6 MiB

What should I try to install on the M910?
How can I find why it does not boot?

Thank you for your help.

Is the boot order correct in the BIOS/EFI?

Did you check your download?

Did you install grub to the correct drive?

Does it work in 'live' mode?

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Its Debian arch name is amd64, not Intel's i5-6400 arch x86_64.

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I had found the AMD64 was the version to use.
The download was correct but I tried the install from CD. Copying the image file to cd was the problem although I did not get a single error message, copying it to usb installed and booted correctly.