I have a quick question about the rules. What is your official definition of "beating" or "finishing" the game?

The usual definition of beating a game in my mind is getting to the credits. This could be through a full completion (100%) or by using glitches (Any%)...

Do you care WHICH credits we get to here? Because there are the "Dog" credits. (In Blackout.)

For almost all categories, "beating" the game is clicking on the alarm clock in Retrospect. If you want to speedrun the dog ending, there's a "secret ending" category in the category extensions page.

You have to finish the game such that the in-game timer says "final time", which you can indeed only achieve by clicking the alarm clock in Retrospect.