Yeah, it varies per game. in NieR Automata's case for example, none of the poll options actually apply in my opinion because there are 26 endings, but I consider it beaten when you've seen the main 5. (an ending for each letter in the alphabet, A-E are the main ones)

Then there are some games where the "all the credits" option would apply in my opinion, such as DQ11 and Trails of Cold Steel 2, where the main story continues after the first credits roll but once you've done the main story you've seen all the credits.

Basically, I consider a game beaten when you've gone through the entire main story. In games with multiple routes but no "true" ending, that means yeah if you've seen the end of one route, i'll consider that beaten. If it has a true ending, I'll consider it beaten when you've achieved that. Fate/Stay Night would be an example of the former, Ever17 an example of the latter.