Review the item:
Jacques, a self-taught computer whiz, always hates going to his Introduction
to Microcomputers class the reason is that
both his textbook and professor are at least a year behind when they discuss
apps or artificial intelligence.
No punctuation of any kind is necessary between is and that. The reason is is a main clause that begins a complete sentence. That both his textbook and professor are at least a year behind is a subordinate clause.
Generally, when you attach a subordinate clause to the end of a main clause, you need no punctuation.