Could Bitcoin switch to PoS like Ethereum? That would also cause Bitcoin’s price to fall.
No never because PoS is a fundamentally flawed protocol.
Not only is PoS a POS (Get it?

) but it is also a way to completely centralise a decentralized cryptocurrency. When Ethereum became PoS, 2 addresses owned 46% of the nodes. That is de-facto de-decentralized (aka centralized).
That is not something we would want for Bitcoin.