Today I have updated Django to latest version 3.1.
But for some reason when the logged in to admin page, all I cans see is a weird looking admin page.
Your browser is caching the CSS / JS from the old version, in which case clear your cache and for that, you need to do Force Reload.
@Tom Carrick, you are right btw.
and to Force Reload in Chrome use Hold the Ctrl key and press the R.
and for Mozill Firefox Ctrl + Shift + R