iternabe I can only manage practicing 1 scale, learn 1 piece, and polish 1 piece in the same day.
That sounds very good!
As for me, how much I work on in a practice session depends on how much time I have, and what I have coming up. For example, when I was preparing for the recital or the concert, that determined my practice sessions, which were tightly focused on the recital pieces of course, and didnโt include new material.
But in general, in a regular practice session, I work on 1-2 pieces that are still in the early learning stage, then I have maybe 2-3 in the polishing stage, and then there are always multiple pieces I want to play for maintenance, so I rotate through those. If I donโt have much time, I just practice the learning pieces. When I have a lot of time, I go through all the pieces, taking one or two breaks (getting up from the piano, stretching my legs, getting something to drinkโฆ)
But I have been playing piano a long time, so I feel more comfortable working on a lot of things at once (or in one practice session).