What does any of that have to do with vetting social media posts for unapproved viewpoints?
What does your previous comment have to do with it?
Inspecting visitor's social media doesn't break the constitution same as how inspecting their/your luggage at the airport doesn't. Border checks are a thing orthogonal to the constitution.
Employers will also Google you and judge you based on what you said on social media. If your profile is full of swastikas or other schizo shit, you probably won't see an offer. Why shouldn't countries do it? Do you want dangerous people let?
So no, that doesn't break the constitution.
I realize that you aren't from the US, so maybe you don't know how US courts have interpreted the first amendment. The US government cannot prohibit "swastikas and other schizo shit", as distasteful as they are. Your employer is perfectly free to do so, however. Those are two different things in the US.
Your freedom of speech ends when you're physically and practically disturbing other people's freedoms. Weird how people don't get that.