Some points to consider
There is an important premise, if a button needs explanatory text,
either below or above, that button is not convincingly complying
- If the text is an explanation of the button's function, the design fails.
I would study the button design from scratch.
- If the text is complementary to the button, I would prevent the design from showing it as an explanation
If the design is unmodifiable, at the perception level, so that a text is interpreted as part of a parent object, the left alignment is a factor against it due to the reading order from left to right: the jump to the next line unlinks them. On the opposite, the central alignment offers a single reading direction, from top to bottom, placing the eye in the center of each object, simplifying the overall reading and consequently grouping them as a single element.
Edit after the comment
Regarding which of the two options is preferable, I don't think it's possible to choose one or the other without knowing the context. As an aid, it may be useful to formally break down the group. Both options form a triangle. Unlike other shapes, a triangle, among other qualities, always establishes a hierarchy: from the tip to the base or from the top to the bottom vertex.
- Option one: the text floats on the button, personally it's the one that I see as the most unstable despite the fact that the triangle rests on its largest base.
- Option 2: the text hangs from the button, I think it's the one that most invites you to click on the button, it is perceived as a projection from the bottom up.
I would choose any option based on the level of importance of each component.
In the global design, option 1 loses balance by having more weight on the right, option 2 is more stable.