I don't think it's obvious that this is Myko's fault. Ideally, the inner spaces should be prioritized over the outer ones, and it can be argued that Saka is in his zone. At the same time, it is worth watching the goal in the replay, and looking at the excellent positioning of the Arsenal players - if you wonder what positional play is, then you see the essence here. One of the purposes is precisely through the positioning to set up the opponents in lose-lose situations.
But anyway, it's worth looking at the positioning of Tarkowski. He is pulled out of the positioning by Martin Ø, and in this way a space opens up between Tarkowski and Myko. Tarkowski makes a classic mistake here, pressing before the pass is played, instead he is deceived by a visual fake. His primary task in that situation is to shift, and cover for the back - lie on the right side of Saka on the goal side. It should also be said that Gana does a terrible job of closing down passing angles.