Mac os I can't install anything anymore?

I have now completely rebuilt my mac. So far everything has been ok, but I haven't been able to install anything just a few hours ago. Install something else. Now the loading bar goes when I no longer open a .dmg (I waited 3 hours, it was twitch, I tried it with google chrome, it didn't work). I didn't install anything funny, I only installed opera, steam, discord and vlc and got everything downloaded from the original website

You have to provide more information. Which Mac, which OS, what can't be installed with which message, can nothing be installed from the App Store?