how to know when TIME MACHINE is not backing up?!

i'm a little astounded to see today that my 4 TB hard drive on my cheese grater mac pro is not backing up to the 6 TB internal hard drive in my mac pro. meaning the last backup was DECEMBER 21, 2019.

is there some little app or something or widget with a little tweeting birdie or whatever that i can put on my desktop and take a look and see when it is not backing up?

i DO now see that i can click on the time machine logo and see the latest backup but can i get any kind of alert when it is not backing up? my laptop used to BUG me every day when it was not backing up for longer than a week or two weeks or something?

are there settings somewhere?

THANKS