A squeaky belt has nothing do with AFM and DFM. Shifting into L9 won't change it. People who refer to that solution are not talking about the noise from the belt. However, I don't think it's a DFM issue because it's only happening on startup, not while the engine is just idling. You indicated you have success with putting the truck in L9 and the noise went away, so it may not be a belt issue for your vehicle. I haven't had the issue where I needed to shift into L9, so that might explain why I didn't notice the noise in your video.
I can't help with the clunk noise. Could be a number of things, none of which I've experienced in my truck, and my truck is parked on an 8% grade, nose down, nightly.
Not only did my belt use to squeak on a cold startup, but also when the engine turned back on while driving after turning off at a red light. Initial repair by dealer was to apply some sort of dry lubricant. It reduced the squeak, but didn't eliminate it. After awhile one edge of the belt wore enough that the squeaking went away. Wearing is indicated on the edge, but isn't severe enough for me to be concerned about breaking. Obviously a pulley is slightly out of alignment with the others, but the belt could be a smidge too wide, too.