TPM 2.0: Windows won't take ownership after upgrade from TPM 1.2 to 2.0.

Did you clear the TPM  and reinstall windows  clean.

Things like bitlocker encryption etc must be off.

You cant use hardware tpm and intel PTT at the same time.

TPM unable to change between 1.2 or 2.0 because TPM is owned

https://www.dell.com/support/kbdoc/en-us/000184894/

Open the Services Desktop App (Type services.msc in the search box, then press the Enter key)
Set the DellMgmtAgent Windows service to Disabled
Stop the DellMgmtAgent Windows service
Set the DellMgmtLoader Windows service to Disabled
Stop the DellMgmtLoader Windows service
Proceed with clearing the TPM

Note: If the TPM is not seen in the BIOS, a hard reset is required to bring it back online. Below are the steps to complete the TPM firmware update on an individual system:

1. Suspend hard drive encryption, such as Bitlocker. See Updating the BIOS on Dell Systems With BitLocker Enabled for instructions on how to suspend Bitlocker.
2. Open PowerShell (click Search in the Taskbar, type Powershell, and click Windows Powershell)
3. In Powershell, type the command “Disable-TpmAutoProvisioning”.
4. Restart the computer and enter the BIOS Setup (F2 during start-up).
5. In the BIOS Setup, go to Security and then TPM (1.2/2.0).
6. Click the option to Clear TPM, then click Apply and then Exit.
7. Once Windows reboots, download and run the TPM firmware update for your system as found on our Support site or follow steps in Using scripting or automation for TPM firmware updates from Dell.
8. This update utility will restart and perform the firmware update at the BIOS level.
9. Once it is completed and Windows has rebooted, open PowerShell and type the command “Enable-TpmAutoProvisioning”.
10. While still in PowerShell, type the command “get-tpm” to confirm the TPM firmware is now on the latest version.
11. Restart the computer to have Windows take ownership of the TPM.
12. Resume hard drive encryption, such as Bitlocker.

Instructions for successfully completing a TPM firmware update for your Dell system are also located in the Installation Instructions area of each specific TPM Firmware Update page on our Support Site . If a TPM firmware update is needing to be deployed throughout an environment, please follow our guide on Using scripting or automation for TPM firmware updates from Dell