Are you saying that you did not see option to enable TPM in BIOS, under Securities section.

Have you try to short the jumper near SATA ports to reset CMOS.

Haswell and Broadwell systems shipped with TPM 1.2, and not all can be updated to 2.0 firmware.

In agreement with Chino.  The 5810 was introduced in 2014 and may not have TPM 2.0.  In the following link, scroll down to Does my PC already have TPM?

@Chino de Oro​ That's exactly what I'm saying. I actually haven't tried the jumper on the board. I will try that and let you know. 

This computer was manufactured in 2018, and I have checked from the spec sheet on Dell website that it has TPM 1.2 chip. Also Dell website says it has. https://i.dell.com/sites/csdocuments/Shared-Content_data-Sheets_Documents/en/al/CSG-EN-XX-ALL-Dell-Precision-Tower-5810-spec-sheet.pdf

I will test the jumper and let you know how it went. 

@Wisefi​ , after you reset CMOS, remember to set secure boot on.

@Chino de Oro​ It didn't help. I know the resetting the CMOS works as all other settings defaulted. I have set also the secure boot to ON. Afterwards I rebooted again in hope for it to show up but it didn't. 

I had a glimpse of joy when I realized that Command | Update wasn't functioning properly on Win11, I did a DOS based BIOS update to A34, but sadly that didn't help too (afterwards I've tried resetting the jumper etc. again but still no luck). This is very dissappointing. TPM Security isn't still visible in the BIOS (>Security)- :(

With a CMOS reset, BIOS firmware settings to UEFI mode, Secure boot is enabled, and it still does not show TPM options under Security section, then it could be that the machine was ordered without TPM originally.  

@Chino de Oro​ It's hard to believe that a 2018 model computer would be shipped w/o the TPM chip.

- Does anyone know where the TPM chip is located on the motherboard ? I guess that would be the best way to make sure that it's installed or not. 

- In the case of it not being installed, I'm just wondering if it can be added as an add-on?

@Wisefi​ , don't know about yours but, on some machines, the physical TPM chip could be presented but the machine was shipped with the TPM in a Hidden or Permanently Disabled state to certain region, countries outside USA.

@Chino de Oro​ In that case, I'm wondering if it's possible to buy a TPM module as an add-on ?

@Wisefi​ , that will depend on your location.