The United States Constitution (Article 1) has these relevant things to say:
... and a Majority of each shall constitute a Quorum to do Business; but a smaller Number may adjourn from day to day, and may be authorized to compel the Attendance of absent Members, in such Manner, and under such Penalties as each House may provide.
This requirement means that at least half of the members and one more of each chamber must be present for the Congress to be able to conduct its business.
Each House may determine the Rules of its Proceedings
This means that each house of the Congress can define the voting rules of the chamber.
and the Yeas and Nays of the Members of either House on any question shall, at the Desire of one fifth of those Present, be entered on the Journal.
This means that "Yeahs" and "Nays" are mandatory options, but it also mentions "one fifth of those Present", meaning that those "voting" and those "present" do not have to be the same.
and for any Speech or Debate in either House, they shall not be questioned in any other Place.
This means that the members' of the Congress speech (including voting) is absolutely immune from any adverse action by anyone else (including - courts).
This all combined leads to a conclusion that while "Yeas" and "Nays" are options that must exist, the voting and the presence are separate concepts in the Constitution when it comes to the actions of the members of the legislature. The prohibition of repercussions for the speech on the floor (including saying "Yeah" or "Nay", or not saying anything at all, or saying "Present") leads to an inevitable conclusion that there could be no law forcing members of Congress to vote.
As such, there's absolutely an option to vote or to abstain (i.e.: make or not make a certain statement) while remaining "present" in the Constitutional sense (i.e.: keeping the quorum, or demanding the vote tally to be entered in the journal).