Thor went through some pretty tough things during Avengers Infinity War, which may have affected his divine abilities.
The events ofAvengers Infinity War have been difficult for all the heroes. In the case of Thor, the situation was particularly badly lived since it was added to many other events which could well have happened. After saving in extremis part of his people, the new ruler of Asgard crossed paths with Thanos who killed Heimdall and Loki before his eyes, before destroying their ship. He then found himself alone, and if he hadn’t run into the Guardians of the Galaxy, who knows where he would have ended up. His misfortunes did not end there. When he found himself once again facing the Mad Titan, he had to face a new difficulty since he missed his shot when he took on the latter with the Stormbreaker. It is therefore without much surprise that we found a Thor completely at the end of the roll in Avengers Endgame.
Powerful as he is, the God of Thunder has gone through a lot of traumatic moments in a very short period of time. As the CBR site points out, this could explain why in Avengers Infinity War it seems to be less powerful than in Thor: Ragnarok, and struggles to stand up to Thanos. Thor undoubtedly did not lose in power between these two films, nor in capacities, but his sanity, his mourning, had undoubtedly already started to affect him as of Infinity war. In this film, he has no time to accept or record what is happening to him, he is forced to act on the spot, to do it as quickly as possible. If we follow this logic, in milder circumstances, his face to face with Thanos might have resulted in a completely different outcome, more favorable to the Avengers. However, one major detail should not be overlooked: the Infinity Stones. The Mad Titan holding them all at the end ofAvengers Infinity War, which already made the battle a little less fair. We just have to hope that the god of thunder will have a little respite in Thor 4, Love and Thunder, and that he will be able to regain all the confidence he has lost.