Time machine will not back up

After upgrading to Sequoia 15.0 I get the message that my iMac mini, M2 is locked. I have not locked it. How do I unlock it, if it locked itself with the upgrade? Below is the message I get. I have an Airport Time Capsule from 2015. When I go to Time Machine settings I get the message that Time Machine is "preparing to back up" with the blue bar going back and forth. I have never had that message before. How do I fix this? Thanks