A big drop-off is the norm for films in their second week. When a fitm opens on 4,000 screens all at once, its to get everything the first weekend. Remember, the longer a film runs in a theater, the lower the percentage the studio gets. This is especially true of blockbuster movies. These films are called "front loaded: for a reason. Since these films have started opening in massive releases, its been the norm. Its very very rare for a film to have a low drop rate in a second week.
I could bring up Top Gun: Maverick, the widest PG-13 release ever, and talk about how that film took until week 4 to fall to the box office grossing weekend that Thor 4 just had in weekend 2. But I realize Top Gun is a rare performing blockbuster.
So let's just look at the box office drops in the Thor franchise:
Thor - 47.2% (3,963 screens)
Thor: The Dark World - 57.3% (3,841)
Thor: Ragnarok - 53.5% (4,080)
Thor: Love and Thunder - 68.1% (4,375)
Let's go a bit further and look at the four Avengers movies + Civil War. Thor is in all of these movies as well:
The Avengers - 50.3% (4,349 screens)
Avengers: Age of Ultron - 59.4% (4,276)
Captain America: Civil War - 59.5% (4,226)
Avengers: Infinity War - 55.5% (4,474)
Avengers: Endgame - 58.7% (4,662)
Now finally, let's break down the average drop by phase. As you can see, Phase three films rivaled the phase one drops while Phase four films are seeing a drop over 9% higher at 64.5% on average. If you can't see something is off in Phase Four from how the rest of the MCU has performed, then you're just looking the other way at this point.
Phase One: -54.3% (6 films, 4,005 average screens)
Phase Two: -57.3% (6 films, 4,044 screens)
Phase Three: -55.2% (11 films, 4,296 screens)
Phase Four (so far): -64.5% (6 films, 4,318 screens)