Interesting because I watch that video and think the complete opposite. Each clip, look at Hojlund's position and tell me honestly how Garnacho was supposed to put a ball in to find him. There's huge amounts of empty space repeatedly and Hojlund is never there.
0:04, blocked by 3 Arsenal players. 0:16, poor cross anyway but blocked by 1 Arsenal player regardless. 0:30, blocked by 2 Arsenal players. 0:36, poor cross but blocked by 3 Arsenal players regardless. 0:42, not in a position to receive the ball, should be where McTominay is. 0:56, blocked by 1 Arsenal player and not in a good position to receive the ball. 1:08, not in a position to receive the ball despite a massive space being open if he was to sprint at full pace. 1:18, not in a position to receive the ball, though this one is probably the most forgivable since Garnacho is cutting in to shoot, despite this you can see there is space there that Hojlund could have run into.
Firstly, I will say that neither player are faultless but in these incidents, it's mostly on Garnacho to find the player and be progressive with the ball.
As a wide player/playmaker, your duty is to create and be
effective. You can do that with dribbling penetration, crossing, passing and shooting. Garnacho is trying to do all of these things without much thought of how to get there or how to best implement it. Look at all the clips, he is pretty much head down and just running and running into clogged lanes and spaces without thinking of what to do next. Garnacho is not finding Hojlund or anyone else because he's not thinking about the next step. Less is more. You don't need to take on and make space down the touchline, you don't need to hit a cross from an disadvantageous area, you don't need to force a shot etc. Once you've made the space and got a defender to respect you, you can recycle the ball to another teammate to move it infield/play one-twos or set himself to either take on again or put in a cross from better footing. If you're not finding your own team mates, can't get a good shot or cross away, then it's a you issue. Amad is the perfect example of this in his 50 or so min appearance; had the ball way less but got into really positive areas and laid the ball off to feet.
Apart from the incident at 25 secs, where I thought Hojlund should have moved closer, there is no consistent pattern you can expect from a wide player like Garnacho to be able to predict where to run. As I've said above, yes Hojlund can work the more effective areas better but there's no rhyme or reason to it. You're looking at the clips like Hojlund can magically teleport into the area when Garnacho himself doesn't even know what he's going to do.
I don't blame Garnacho because everything that's he done up until this point has been successful for him as ETH can't coach an attacking (or defensive team). Therefore, he will let players like Bruno, Rashford and Garnacho spam their attacks. Hojlund is just catching the strays of playing in this idiotic set up.