Looking for a noun, a person who changed their past view to a new one [duplicate]

You might be looking for

Hypocrite:

A person who acts in contradiction to his or her stated beliefs or feelings. (merriam-webster)

flip-flopper
a person, especially a politician, who suddenly changes his or her opinion or policy.

https://www.oxfordlearnersdictionaries.com/us/definition/english/flip-flopper

Phony seems like it might fit your example sentence, specifically the "insincere" element.

Phony:

an insincere, pretentious, or deceitful person

That gives more of the impression that they are saying what they think the other person wants to hear, rather than actually changing their mind.

Maybe opportunist is the word you are looking for:

a person who takes advantage of opportunities as and when they arise, regardless of planning or principle.

An opportunist (Collins) will behave differently in different situations, and takes advantage of any situation in order to gain money or power, without considering whether his/her actions are right or wrong. Another dictionary (Wordhippo) defines it as

Someone who conveniently changes opinions, typically for personal gain.

If you check the last link, you will find many synonyms of it, so if "opportunist" is not the one, maybe you will spot the word you need.