Yes. The environment and time is controlled by your employer to maximize productivity for the business. You're free to do whatever you want on personal time, including not working for a company you don't like.
Usually people making your argument also say that private corporations can and should moderate speech. Do you support that? If so, then why do you disagree with workplaces banning topics?
You're misunderstanding the concept. Individual freedom means you're free to make your own choices and then take responsibility for those choices. This freedom is protected by your rights granted by the state.
Corporations setting workplace rules have no impact on your freedoms. You're free to work there or quit, or suffer the consequences of breaking their rules.
Usually people making your argument also say that private corporations can and should moderate speech. Do you support that? If so, then why do you disagree with workplaces banning topics?