Can someone who begins a voluntary fast break it?
It is preferable for someone who begins an act of worship not to break it.
Allah the Exalted has said {what means}: "and let not your [good] deeds come to nought!" [Muhammad/33].
However, if a person starts a voluntary fast (nafl) and needs to break it, they are going against what is preferable, but there is no sin upon them.
Is it permissible to slaughter one animal as a sacrifice and an Aqeeqah (the sheep slaughtered on the seventh day from the child`s birth)?
It is impermissible to do so since each of them is slaughtered for a different reason.
What do you say about someone who stays up all night on Laylat al-Qadr but misses Fajr prayer?
Such a person has deprived themselves of a great reward. Performing obligatory acts is more beloved to Allah than voluntary acts. Fajr prayer is an obligation, and performing it in congregation is equivalent to worshiping for the entire night. So how can someone neglect it while striving for voluntary prayers?!
Does undergoing surgery under anesthesia break the fast?
Anesthesia itself does not break the fast because anesthetic gases have no physical substance (jirm), and subcutaneous anesthesia injections do not reach the body cavity (jauf). However, this is on condition that the person is conscious at some point during the fasting hours:
● If they were awake at the beginning of the day, their fast remains valid.
● If they wake up even for a moment before sunset, their fast is also valid.
However, if the surgery involves the entry of foreign substances into the body cavity, their fast is invalidated, and they must make up for that day later.