Time Machine will not backup

MariaLoLee wrote:

I used Time Machine to back up my Mac onto my new Seagate external 3tb drive. It worked the first time and now I cannot back up again. It seems like Time Machine turned it unwritable. I have another section on the hard drive that I partitioned for other use and is writable. But the Time Machine portion is now not backing up to the the Time Machine partition anymore. I used first aid and it says all fine. It also says it's writable. It goes for hours preparing for back-up and then comes back with an error. What do I do? I appreciate any help.

In partitioning it is good to have TM as the 1st partition— so TM can find the drive...

Types of disks you can use with Time Machine on Mac - Apple Support

Trouble Shooting—

https://support.apple.com/guide/mac-help/time-machine-troubleshooting-mh15653/mac

Lately I have found TM formatted to APFS likes to be dedicated only for TM and issues arise when using the drive for something else as well especially since using Big Sur. Also having other files on TM is note safe . I would have two different drives.

I would have one drive for dedicated TM about 2x your internal drive size. Use disk utilities and format to APFS (Big Sur will not do this also automatically if only using for TM). Then get another drive to use for files, etc.