I almost never use the login window at boot (leave it on automatic login), so didn't notice any difference at first.
You have your Restart, Sleep, and Shutdown buttons turned off, I suppose.
You can change that setting in your Users & Groups/Login Options.
That's what I suggest is to turn that option back on, then restart to see if there is any change in the login window.
Or, check your Displays, and make sure your settings are Default for your display, and not scaled.
Try a restart again, to see if that makes your login normal for you.
You can always change your display settings to what you prefer (if it is different), and then just expect that the login window looks slightly different now.
Sometimes changing the display settings will "reset" the login window, and then it will stay "fixed" for you. I can't tell you that really will be the result. I just know what I see. You get fixes sometimes just by changing one or two relevant settings, restarting, then changing those same settings back to your normal.
It's a common troubleshooting step for some kinds of issues.
