That is only an opinion held by a few. Even the 7 democrats on the court couldn't agree on this. Trump has not been convicted or even charged in this allegation.
No person shall be a Senator or Representative in Congress, or elector of President and Vice President, or hold any office, civil or military, under the United States, or under any state, who, having previously taken an oath, as a member of Congress, or as an officer of the United States, or as a member of any state legislature, or as an executive or judicial officer of any state, to support the Constitution of the United States, shall have engaged in insurrection or rebellion against the same, or given aid or comfort to the enemies thereof.
An officer of the United States is Under the Appointments Clause of the Constitution, the principal officers of the U.S., such as federal judges, ambassadors, and "public Ministers" (Cabinet members) are appointed by the President with the advice and consent of the Senate, but Congress may vest the appointment of inferior officers to the president, courts, or federal department heads. Civilian officers of the U.S. are entitled to preface their names with the honorific style "the Honorable" for life, but this rarely occurs. Officers of the U.S. should not be confused with employees of the U.S.; the latter are more numerous and lack the special legal authority of the former.
Nowhere in this amendment is the president or a candidate for president mentioned.
150 Confederates served in congress after this amendment was passed