Catalina Time Machine: Past explanation for "Out of Space" is incomplete
The discussion of "Out of Space" in a previous question states "Once Time Machine finds it cannot free up enough space for a new backup it reports the disk is full. You can either erase the backup drive and start over or get a larger drive." This fails to get at the problem: What's wrong with the design of Time Machine that it can't reliably keep discarding the oldest incremental file? Relatively few files actually change over time--it shouldn't take much space to track that.
I have a TM drive that is 3 times the size of my system drive. If TM were working properly, it should just hum on forever. But instead, I keep getting the message Backup Failed, Out of Space. With 453 Gb free, how is it possible that TM can't do an incremental backup?
BTW, I've had a continuing problem since Sierra: "Entering TM" produces a black screen, without the stacked windows. I'm able to get the standard TM screen to appear for only a second as I close this. What's up?