I think Max-Q occured about a minute before. You can review the stream, it passed supersonic way before (you see the shock cone on the two sides), then max-q, then a minute later the explosion

same feeling here. anyway, you could see the cap going off before rocket was self destructed. dunno if was part of the sequence.

the engine exhaust plume expansion reminded of that time they lost a nozzle due to high pressure, but again hard to tell if it was cause or effect from the armchair

Indeed it was around main engine cutoff.