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Referring to this post, in the following formula to update the state-action value

$$ Q(s,a) = Q(s,a) + \alpha (G − Q(s,a)),$$

is the value of $G$ (the return) the same for every state-action $(s,a)$ pair?

I am a little confused about this point, so I will thank any clarification.

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The discussion uses poor notation, there should be a time index. You obtain a list of tuples $(s_t, a_t, r_t, s_{t+1})$ and then, for every visit MC, you update

$$Q(s_t, a_t) = Q(s_t, a_t) + \alpha (G_t - Q(s_t, a_t))\;;$$

where $G_t = \sum_{k=0}^\infty \gamma^k r_{t+k}$, for each $t$ in the episode. You can see that the returns for each time step are calculated for time timestep onwards, and so are not necessarily the same across time steps.

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