From my understanding, Turing complete means that the program or machine can complete any computation that a Turing machine can complete, which to me means any computation. So how can something like HTML or PowerPoint be Turing complete?
Some system is Turing complete if you can simulate every Turing machine inside of it. Powerpoint is Turing complete because its animation features can be used to simulate a Turing machine. This video explains the proof for Powerpoint. You can read the proceedings from the 2017 SIGBOVIK for a written explanation.