Pro forma sessions are meetings of the U.S. Congress held “in form only.” Either house of Congress can hold pro forma sessions.

During pro forma sessions, no votes are taken and no other legislative business is conducted.

Pro forma sessions are held for the purpose of meeting the “three-day rule” in Article I, Section 5 of the U.S. Constitution. The three day rule prohibits either chamber of Congress from not meeting for more than three consecutive calendar days during a congressional session without the approval of the other chamber.

Which has never been done before.

that explains whether TSF should be allowed to adjourn Congress.

If the House were to adjourn and the Senate not adjourn, Trump backers are claiming that would be a disagreement of Congress as to the time of adjournment and TSF can step in and adjourn Congress.

The author of the article I linked believes that scenario should not be considered as a disagreement of when to adjourn.

Sadly, there is no precedent since no president has ever invoked it.

https://www.cato.org/blog/disagreement-presidential-power-adjourn-congress