Withholding or withdrawing therapy that can keep someone alive–is a more complicated issue. The Talmud forbids all acts that might hasten death,
and this ruling was upheld by the medieval Jewish law codes.
However, in a famous passage,
the 13th-century Rabbi Judah the Pious ruled
that one should remove obstacles which prevent death.
Rabbi Moshe Isserles codified this ruling
in his commentary on the authoritative 16th-century law code the Shulhan Arukh,
writing that,
“if there is anything which causes a hindrance to the departure of the soul…
it is permissible to remove [it] from there because there is no act involved,
only the removal of the impediment.”

See here