Does the reward for good deeds such as prayer, charity, reciting the Quran, and remembrance of Allah increase if a Muslim performs them while observing a voluntary fast, and what is the evidence for that?

There are indications in the Sunnah that the virtue of worship increases when accompanied by fasting. The supplication of a fasting person is not rejected, and in Paradise, there are chambers for those who regularly fast. The Prophet, peace and blessings be upon him, was most generous during Ramadan, and it is recommended to increase generosity in Ramadan, following the example of the Prophet, peace and blessings be upon him. It has been reported that the sleep of a fasting person is worship, their silence is glorification, their deeds are multiplied, their supplication is answered, and their sins are forgiven, though the chain of narration for this last hadith is weak. The meaning of "multiplication of deeds" is that a good deed is rewarded tenfold, and "forgiveness of sin" means that minor sins are forgiven by abstaining from major ones.