More precisely he is like an influencer, he can have a big effect on the movement of bitcoin, with the achievement of acquiring Twitter and with his tweet weapon, he easily makes bitcoin price change in a short time. I think it will be terrible for the future of cryptocurrencies.
He is considered as an influencer because he is famous and have lots of followers but it's not bitcoin, it was doge or shib are the ones that he will promote. Elon already ended its connection with btc because btc is not friendly to the environment therefore there is nothing to worry about.
Whatever happens to those meme coins won't have any effect to bitcoins but manipulations is not all about dumping the price or making it more volatile but pumping can happen as well. Those meme coin hodlers are going to be happy if that happens because finally they can now recover what they lose or possibly earn more but we btc users shouldn't be jealous with that as that is only temporary.