Yes, but with limits that you aren't acknowledging exist.
The 1A covers more than just speech, but with regard to speech, the government can't restrict it in public venues... but again with limits. In private venues, the government has no say either, but with limits.
Everyone is free to ignore you for any reason they choose--perhaps they would choose to do so because of your insulting ignorance.
It's illegal to incite a riot or other crimes anywhere in the U.S., through speech or other means, whether in public or private. It's illegal to yell "fire" in a crowded theater when there is no fire. Any "speech" involved in the perpetration of fraud or other crimes is illegal everywhere.
Potential advertisers are free to choose to support a private platform like Twitter... or not to support it. As owner of Twitter, Musk can choose to allow/disallow any speech or users he wishes. Section 230 of the US civil code means he doesn't have to worry about being responsible for users inciting criminal behavior, spreading disinformation, or hate speech on the platform. But users and advertisers are free to go elsewhere if he doesn't effectively handle this crap.