Can you score the last point with an alternate condition like Tryndamere - Barbarian or Yasuo - Windrider?

Yes, you can score the final (8th) point to win the game using alternate scoring conditions like those found on Tryndamere, Barbarian or Yasuo, Windrider.

According to Rule 448.1.a.1, points earned from sources that are not "Conquer" or "Hold" are not beholden to the final point restrictions (such as needing to control both battlefields or having scored all battlefields that turn). These alternate scoring effects function as direct paths to victory.

Here is how they apply:

• Yasuo, Windrider: You can score the final point by triggering his ability (the third time he moves in a turn). This bypasses the standard battlefield scoring restrictions.
• Tryndamere, Barbarian: His ability allows you to score a point when you conquer after an attack and assign 5 or more excess damage. Because this is a specific ability-based point, it can be used to reach the final point total.

Important Nuances:

• Restriction Scope: The restrictions requiring control of both battlefields or holding only apply to scoring points directly from the battlefields themselves (Conquer/Hold).
• Tryndamere's Specifics: Note that Tryndamere's ability triggers "When I conquer after an attack." This means he must be the Attacker for the conquer action to trigger his ability. If he is brought in as a defender (e.g., via a card effect), his ability will not trigger.