If God, Jesus, the devil, angels, and demons were all real, we still couldn’t rely on the Christian Bible as gospal (pun intended) — it was written by humans, specifically men, who could have misunderstood or invented things. Think of it like the Snyderverse in Man of Steel: Superman is portrayed as a brooding, violent character — but that’s not his true nature. In Batman v Superman, Batman is straight-up killing people — also not his normal characterization.
So even if much of the Bible reflects real events or real beings, parts of it could still be distorted, exaggerated, or entirely made up by the people who wrote it down.
Surah 3 (chapter of quran) discusses the birth if Jesus and the the prophets before, who were given Torah and the other revelations. As I’ve understood they are considered true and from the same divine source, however have been muddied over time and hence the last and complete revelation is needed and given via the prophet Mohammed.
Then after his death, people were divided between whether to follow his divine bloodline (Shia) or his way of life (Sunnah) and they tried to capture all information about his life and teachings which were not in Quran (Hadith). The 5 daily prayers for example are not explicitly mentioned in the quran.