Does showing my opponent I have an effective win condition qualify as improperly determining a winner?
The key phrase in that rule is in the first sentence:


  A player uses or offers to use a method that is not part of the current game (including actions not legal in the current game) to determine the outcome of a game or match.


Importantly, it is not a violation of this rule to take an action that is legal in the current game to determine a winner. For example, Magic Tournament Rule 3.12 says in part


  players may choose to reveal their hands or any other hidden information available to them, unless specifically prohibited by the rules.


So, it would be perfectly legal to determine a winner by having a player reveal a card from their hand.



Regarding the specific examples:


At that time, Alice is not legally allowed to search through her deck, so determining the winner that way would violate that rule.
The decklist slip is not part of the game, so using it to determine the winner that way also violates that rule.
Alice's statement that she cannot legally show a win condition is correct. Bob is allowed to choose to concede at any time. Alice is allowed to lie about the existence of a win condition, according to the commentary on Magic Tournament Rule 4.1:


  Private information is the catchall category for everything that is not free or derived information. For example, the contents of hidden zones (i.e., library and hand) and the identity of face-down cards in public zones are considered private information. Players are allowed to give their opponents false information about the contents of a hidden zone. ...


So, every part of this example is perfectly legal.