iMessage Login Loop

Since updating to Big Sur, I have had problems logging into iMessage and FaceTime. I also have had similar problems with the App Store since Catalina.

On iMessage, it lets me log in but logs me out 10 seconds after opening. I also can't access Preferences. I have restarted my computer (several times) and signed out of my Apple ID, but nothing changed.

On FaceTime, it doesn't let me login at all. It just loads then asks me to login again.

I have had similar problems with getting updates on the App Store since Catalina though the problem has changed slightly. On Catalina, when I tried to update iMovie for example, it asked me to sign in to the iTunes Store with my Apple ID (though I was already logged in), then told me to sign in over and over without doing anything. On Big Sur, I am logged in and push the button to update. Then it asks me to sign into the iTunes Store with my Apple ID, giving me a text box to do so. I do, then it says, "Sign in to the iTunes Store" with no text box and gives me the two options, "Cancel" and "Download." Clicking download, the same request pops up. After 4 times of this, it just does nothing.