Time machine hanging

Greetings, tatltuae.

I see that you're unable to complete a Time Machine backup of your iMac since upgrading to macOS Mojave. I'm happy to help.

If a Time Machine backup takes longer than you expect

Backing up large changes

Some backups might take longer than others if you've made changes to a lot of files, or changes to large files since the last time you backed up. You might see ”Preparing” in the Time Machine menu for a longer period of time when this happens. For example:

• When your backup disk isn't available (such as when you're traveling, or your backup disk is disconnected or powered off) Time Machine can't back up your files. If you use your Mac for several days without access to your backup drive, it might take longer the next time the drive is available.
• If you're using virtualization software on your computer, such as Parallels or VMWare, that software might create a large disk image or other file to store data related to other operating systems. Time Machine might try to back up the whole disk image, even if you've only changed a few files on it. For best results, make sure your software is up to date, then check the developer's support site for information on using Time Machine with these apps. If you want Time Machine to skip these files, you can also tell Time Machine to exclude them from your backup.
• If you recently installed new software or upgraded macOS, it might take longer to complete the next backup. After Time Machine finishes backing up your new software, backups should be faster.
• If you canceled or unexpectedly interrupted the previous backup, Time Machine might take longer the next time it backs up your files. This can also happen if you don't shut down your Mac properly, or if you don't eject a drive before disconnecting it.

Take care!

Even if it started looks like there is a TM issue that makes TM not work properly:

Mojave time machine back up failing