Sergio is flying downwind in that clip and still has to correct a stall now and then. The other guy is generally going downwind, but also sort of tooling around in place on a broader reach.
Bar trim is dependant somewhat on wind strength but mainly on what line wrt the wind you want to ride. For deep downwind wave riding you can have the kite more powered, for a broad reach or any kind of upwind line you will need to depower the kite. Even with peaks heading down wind, the goal is to have the kite just drift light in your hand. Powered up it will be pulling. Again, different in 10 knots than 15. As seen in both clips. You can recover the kite from a stall when it happens (kite gets too deep in the window) by pulling on the chicken loop. With some skill you can keep your relative position to the kite wrt the wind window workable without having to do any pulling on the front lines, but it takes a little practice and dictates your line. You really need to understand the basic dynamics of trimming for unhooking and riding that way before you try it foiling. Playing around with trim unhooked on wide open beaches or on snow is where to start. For those already skilled at unhooking, it’s not very hard to do foiling. I have 4 bars for foiling and "can" unhook on all of them, but only the one on the peak 5 and the chicken loop set up have trim cleats. IMHO you really need that cleat to have any fun unhooking.
* related, but not unhooking per say * The SS bar without CL is a light wind dedicated bar, longer lines, no cleat, set to full power without back stall. I ride that on a longer tether to the harness so at comfy arms length for working the kite in loops it is at full power, bar sheeted all the way in resting against the red release, more or less like being unhooked, the kite working as a static non depower kite. Definitely easier to waterstart on the low end when you have full power pre set and can't oversheet. Once up and riding there is plenty of depower in easy reach. Highly recommend this for maxing the low end fun on your Peak4.
I have swapped the board riding maui style push ball releases for these cabrinha mushroom cap push releases as they are much easier to hold onto unhooked and they prevent the pin from damaging the bar. Can unhook and generally hook back in with these while riding but it takes two hands and a table enough kite that you can let go of for a few seconds at a time. The stripped down chicken loop bar is much easier for unhooking in more demanding conditions.