Time Machine backup silently fails. Log says "Backup canceled."
Try clearing some space on the origin drive you are attempting to backup.
I have seen Time Machine logs similar to this when Time Machine is having trouble organizing things within the space available on the origin drive. Often several GB are needed (I don't know why). So if you can get your drive to have more than 40GB of free space then do that.
By the way, using log stream --predicate 'subsystem == "com.apple.TimeMachine"' --info --debug labels lines that are considered errors a little more clearly.