Satan is the personification of the worst of evils: that of vanity.
Not just looking in a mirror and calling yourself beautiful, real vanity is very specific. It means comparing yourself to God and claiming god-like powers beyond what you are.
In the philosophy of the Pentateuch, God is the creator of all things. He does this directly, not through agents or representatives, though is not exclusive about the maintenance or manipulation of His creations.
Mankind performs its own function within creation: that of labeling and describing creation with abstracts. But neither angels such as Lucifer, nor mankind, can create anything. Everything we seemingly create is either just maintenance or manipulation or description of what already has been created.
As such, the pretense and assertion that we do create is the oldest of sins. Vanity is also the one sin resulting most consistently in punishment in the Pentateuch. While the assumption is that this punishment is “from Heaven”, it could also be imagined that vanity creates its own punishment without the need for Heavenly intervention.
Philosophers have never been happy with the idea that God is the exclusive creator, because they crave for mankind to be part of the process of creation. Unless mankind can “do” creation, there is little for philosophers themselves to do. So over time, philosophy tends to become atheist.
Did Lucifer exist? Does he still exist as Satan? Good questions. But even if he is no longer, he still performs a very useful role of reminding us of the hazards of vanity. His manifestation is all about vanity, of a very specific kind.
I disagree. Jesus spoke of Satan as an actual being.
A keyword search of Satan revealed quite a number of references to him and his activity.
https://www.biblegateway.com/quicksearch/?search=satan&version=ESV&searchtype=all