He had 6 weeks off but since January his game has definitely changed slightly, more involved in the buildup and he's pressing better/more frequently.
I agree defenders are literally man marking him now but we're still creating 3/4 chances per game that he should be converting, you can see he's rushing his shots and/or overthinking them. He's scored 60+ goals this season so its not down to a lack of confidence or ability, it has to be fatigue, a mixture of mental and physical.
At Dortmund he's never been in a title race or reached the semi-final of UCL, that comes with added pressure especially when he's basically the star of the team, at 22 he keeps in good shape and will never ask for a break but its clear he's lacking sharpness.