How to check if used Samsung Galaxy S23 has original bootloader, firmware, and software?

I bought a used Samsung Galaxy S23 from a large online seller. How can I check that all the software and firmware is original and not tampered with? I already did a factory reset from the settings menu. I'm wondering if there's a way to check the bootloader, firmware and other important systems. I tried rebooting into Download-mode (phone off, hold both volume buttons and plug in USB power), and the Knox status says KG STATUS: CHECKING(00). It never updates away from "CHECKING". Note that I don't have a SIM card yet. The phone was sold as originally Verizon locked but is now unlocked.