Biblical and Rabbinical regulation-Food must be able to be benefited from on Yom Tov and is done for the sake of Yom Tov:[1]

All the Melachos of Ochel Nefesh were only permitted to be performed on Yom Tov for the sake of benefiting from it on Yom Tov. It is however forbidden to bake, slaughter, and cook on Yom Tov for the sake of eating it after Yom Tov. One who does so, transgresses a Biblical prohibition and is liable for lashes.[2] This however only applies if the Melacha was done on Yom Tov near evening in a way that one cannot benefit from it at all on Yom Tov itself [do to there not being enough time to receive the benefit]. If, however, it is possible for one to benefit from the food on Yom Tov itself, then he is exempt from a Biblical transgression even if he does not plan to benefit from it on Yom Tov and intended to do the Melacha for the sake of eating the food the next day.[3] Nevertheless, the Sages prohibited this to be done, and one who does so is liable for Rabbinical lashes.[4] [Accordingly, it is Biblically forbidden to perform a food related Melacha on Yom Tov if it is being done in a way that the food cannot be benefited from on Yom Tov, and it is Rabbinically forbidden to do so even if he can benefit from it on Yom Tov, if his intent is for the next day.] Thus, one who bakes, slaughters, cooks or does any other Melacha towards the leave of Yom Tov, for the sake of eating after Yom Tov, [and it is not possible for him to benefit from the food on Yom Tov itself due to it not being ready], transgresses a Biblical prohibition.[5] This Biblical prohibition applies even if Shabbos falls after Yom Tov, and one is doing the Melacha to the food for the sake of Shabbos.[6]

____________________________________________________________________________

[1] Admur 495/2 “For the sake of eating on Yom Tov”; 503/1-2; 527/8; M”A 518/1 “One who cooks on Yom Tov for the weekday gets lashes”; M”B 527/3; Rambam Yom Tov 1/9; Beitza 17a; Pesachim 46b; See Aruch Hashulchan 527/3; Piskeiy Teshuvos 527/3 for other opinions in this matter

[2] Admur 503/1

[3] Admur 503/2; M”A 527/1; Tosafus Pesachim ibid

The reason: Even if the Melacha is not needed at all for Yom Tov, being that one already ate all his meals in entirety, it is nevertheless only Rabbinically forbidden. The reason is because if he were to receive guests that did not yet eat that day, then this Melacha would be considered a need for the guests, and would have been permitted to be performed by him. Therefore, this Melacha is called Mileches Ochel Nefesh, and even though he does not have guests, its performance does not contain a Biblical prohibition. [Admur ibid; Pesachim ibid; Rashi on Pesachim ibid]

[4] Admur 503/2; M”A 527/1; Razah Pesachim 14b; Ran ibid

[5] Admur 503/1

[6] Admur 503/1; M”A 527/1; Raba in Pesachim 46b