TPM and Secure Boot
A PC may support TPM or Secure Boot even when the setting is disabled in firmware. A good checker should label unavailable information instead of guessing.
CPU and firmware
Processor eligibility depends on Microsoft's supported-processor rules. The safest approach is to identify the exact CPU model, then confirm it against current requirements.
Before changing settings
Back up important files and understand firmware changes before enabling TPM, Secure Boot, or UEFI-related options.