Hi:
Your HP dc7900 has a legacy BIOS.
It does not support UEFI or secure boot.
You need to have an HP 8300 Elite or newer PC to have both of those options.
In order to run W11, for the current requirements you would need the equivalent Elitedesk 800 G4 .
If you want to test W11 on your PC, you should be able to do that now by enrolling in the Windows Insider program and selecting the developer option.
You can do all of that from the PC settings menu>Windows Insider program.
But once W11 is released to the public for general use, you will need to reinstall W10.