Having seen the video, it looks like your derailleur is MASSIVELY outside of it's B-tension adjustment. Put it on the biggest cog and turn the B-adjustment screw to the point where the top cog of the derailleur is about 3-4mm away from the cog. In my personal experience, this is a common cause besides the actual indexing, and it looks quite likely here, too.
Also, that chain looks a bit big for an eleven-speed set-up; Is it original? Also check for chain wear, as this will cause a horrifyingly loud sound, along with wearing out the cogs faster.
Also, and this might sound a bit basic, but please bear in mind we have all skill-levels here;
Is the wheel properly aligned within the rear drop-outs? The wheel on the derailleur side needs butting up against the very furthest point of the drop-out, or rather, shoving in as far as it'll go. The drive-side is used to make sure the wheel is A) grabbing onto a safe amount of material and B) to essentially 'zero' the alignment for the cogs, and where they sit inside the frame.
Remember, the adjustment screws on the derailleur only adjust where the derailleur will sit within the frame, not where it'll hit the cogs. You can use the old-style method of measuring the gap between the frame and where the first cog would be, and then measure the distance of the first and last cogs, then adjust the tension of the cable to make it evenly move around the range, and have a perfect derailleur adjustment, you don't actually need the wheel within the frame to do an indexing. However, it is recommended for less experienced to just do it with the wheel on, and it also helps with fine-tuning.
After checking the wheel's alignment, make absolutely certain that the springs on the derailleur are moving easily, with no noise, and without requiring cable tension to be dropped to near zero. They should only need a slight tension adjustment to make a fairly drastic gearing change.
Good luck with the repair!