Boot Commands not working (can't get to Startup Manager)

You can try using an external USB keyboard to see if you can then Option Boot the laptop in case there is an issue with the built-in keyboard. I have seen a few Apple laptops with a Logic Board failure where keys may work while booted into macOS, but may not work during the startup process (or even the other way around).

You can also just install macOS from Internet Recovery Mode. In theory if you use Command + R it should present you with the online installer for the most recent OS you were using on the laptop. Otherwise you can install Catalina/Big Sur (depends if you have the early or late model) using Command + Option + R. If you need an OS before Catalina/Big Sur, then boot using Command + Option + Shift + R to boot the installer for the OS which shipped from the factory on this laptop. Of course if there is an issue with the built-in Keyboard or the Logic Board, then these other Internet Recovery Mode options may not work. Plus these options don't always work correctly as sometimes a Mac will only boot to the installer for the original OS.

Also in theory if there is no OS at all on the internal SSD, then the laptop should automatically boot to the USB boot drive (assuming it is a valid macOS boot drive and was correctly created) if no internal boot volumes are found (especially if the PRAM Reset worked).