I think there is nothing strange about Alvarez's performance in La Liga with Atletico Madrid. Alvarez needs time to adapt to his new team and also to different competition, after all Simeone's playing strategy is also different compared to Pep Guardiola at Manchester City. Alvarez shouldn't need too many matches to prove his quality, but in 4 matches he hasn't scored a single goal or assist.
Alvarez is actually in very good position this season, and if his given the time he needed sometimes it takes time for some players to adopt with their new club, and it is always different for each players, and Atletico Madrid was even able to defeat girona, and the method of the leagues are different and but even still he will adopt over time. And any player that pep have trained will always adopt every were they find their self, and during training he should a start adapting from their, then when it comes to games to his performance will continue to build up, with his new family and now, and Their is a lot of expectations from him since his coming from Manchester city, the air is fresh but the expectation will always be their.
On the other hand, Alexander Sørloth has also had 4 matches this season with Atletico Madrid. The difference is, Alexander Sørloth has scored 1 goal and 1 assist in 4 appearances, different from Julian Alvarez. Diego Simeone has been responsible for supporting Julian Alvarez's adaptation since he was brought in from Manchester City, but if Alvarez's performance does not improve then he will have to accept the reality of being on the bench for longer.
Alexander Sørloth performance is not yet satisfactory because, scoring one goal and just one assist, and I feel he should do more, and scoring just one goal in four appearances is not a good sign then when the season becomes serious how strong will his performance be, and if his the one supporting Alvarez's then they still have to come up with a better strategy to penetrate because this is not a period to actually be test running the season have fully started and goals are needed to make points.