אף על פי שהתשובה והצעקה יפה לעולם בעשרת הימים שבין ראש השנה ויום הכפורים היא יפה ביותר ומיד היא מתקבלת שנאמר דרשו ה' בהמצאו קראהו בהיותו קרוב.
So the Rambam of course quoting, presenting from the Gemara in Rosh Hashana, but the formulation k'darko is very nuanced. The Rambam begins with a compound subject, אף על פי שהתשובה והצעקה יפה לעולם. So he's talking about both teshuva and tze'aka, and talking about how the period of aseres yemei teshuva is especially mesugal for both. Again, clearly the pshat in the pasuk of darshu Hashem behimatzo refers to teshuva and kara'uhu bihyoto karov at the same time of year refers to tze'aka, refers to tefilla. But what's so interesting here is that even though the Rambam begins with that compound subject of התשובה והצעקה יפה לעולם, he says בעשרת הימים שבין ראש השנה ויום הכפורים היא יפה ביותר ומיד היא מתקבלת.
Then the Rambam switches to the singular. What's more, the verb that he uses of miskabeles is more reflective of the teshuva. Ve-haraya in the Sefer of the Halacha where he contrasts the tzibbur: ובציבור כל זמן שעושין תשובה וצועקין בלב שלם הן נענין.
When it comes to the tzibbur who are not limited to aseres yemei teshuva, so the Rambam says they are always na'anin reflecting the tefilla. So the impression you have in the Rambam is as follows: that the tze'aka of which he's speaking of aseres yemei teshuva is a tze'aka which is an integral part which accompanies the teshuva, not sort of an independent free-standing tefilla, but rather a tze'aka primarily focused on kabbalas hateshuva, on asking HaKadosh Baruch Hu to receive us back, to receive our teshuva, to receive us back as per earlier in halakha daled מדרכי התשובה להיות השב צועק תמיד לפני ה' בבכי ובתחנונים.
So it's takeh the pshat, it's a zman for both teshuva and tze'aka, דרשו ה' בהמצאו קראהו בהיותו קרוב, but ultimately it's miyad hi miskabeles, the tze'aka focus is a request for kabbalas hateshuva, miyad hi miskabeles. Gemar chasima tova.