What the video calls "debounce" is just an autorepeat delay. And on AT and PS/2 keyboards it is not done by any kind of PC side software (neither driver nor key

What the video calls "debounce" is just an autorepeat delay. And on AT and PS/2 keyboards it is not done by any kind of PC side software (neither driver nor keyboard controller firmware), but by the keyboard itself (In late 90's/early 00's there even were PS2 keyboards where you can set the rate manually with key combination). In the protocol layer, autorepeat works by repeating the key down event without key up events in between, so if you are interested in state of the key without the autorepeat you can simply ignore key down events for keys that you already see as down. The real debouncer hardware is also in the keyboard itself for all standard external keyboards ever used with PC. On the other hand there were simple keyboard interfaces which involved reading out the whole keyboard as if it was one big shift register and debouncing was then done on the host side in software, two examples from top of the head are Symbolics machines and Wyse terminals. Interface for (S)NES controllers (really for Nintendo controllers up to GameCube) is similar, but I'm not sure whether debouncing is done by controller hardware or not.