Mongbrains that think they understand how to interpret the finer details of the constitution are always amusing. Do you know what common law is? It's a basic principle that you have to understand, particularly with regards to the state of common law when the constitution was written, before you can figure out whether or not something actually is constitutional.

From one article on the topic -

"Richards explained that the colonies frequently practiced isolation in an effort to keep out infectious diseases... They were very deeply enculturated into the society,” Richards said. “There are not many Supreme Court cases directly on the point because the law was so well established that no one would have thought to challenge it.”

But, as implied there are in fact cases dealing with this matter, such as the ones described in this other article on the topic

"The most significant early decision from the U.S. Supreme Court to mention the state power to quarantine occurs in an 1824 case known as Gibbons v. Ogden. Considered a landmark decision on the federal power to regulate commerce on the interstate waters, Chief Justice John Marshall — our greatest chief justice; the competition is only for second — explained that one of the powers the state possessed was the power to quarantine.

This was not controversial; as Marshall put it, the power to quarantine was seen as a power “flowing from the acknowledged power of a State to provide for the health of its citizens.”

He then goes on to list other cases, which also affirm this. All you had to do was a simple google search and you could have gotten a correct answer to this question. Yes, during a pandemic the state can ban activities that would normally be constitutionally protected. But hey maybe if you write a letter to Justice Kennedy that you've noticed this "right to peaceably assemble" passage that the other Supreme Court justices seemed to have missed, he'll look into it.