If Time Machine takes a long time to back up
Time Machine is designed to work in the background, without interfering with the regular operation of your computer. Time Machine backs up only the changes since your last backup, so after your first backup, future backups should be faster.
Check for large, frequently updated files
Some apps store data in unusually large files that the app updates frequently. Backing up such files can be time-consuming, and Time Machine backs them up every time it sees that the file has changed.
Or contact the app developer to learn how to best use their app with Time Machine.
Check for apps that keep your backup disk busy
Some apps, such as antivirus utilities, might keep your backup disk busy by frequently accessing the disk to find items or save items. Find out whether the app's settings can be changed prevent that, and use your Time Machine backup disk only for Time Machine.
Connect the backup disk directly to your Mac
If you're using your Time Machine backup disk over a network, backup speed is affected by the performance of your network. You might get better performance by connecting the backup disk directly to your Mac.
Upgrade macOS and use an APFS-formatted backup disk
If you're using the same Time Machine backup disk that you were using before upgrading to macOS Big Sur or later, follow these steps:
Make sure that you're using macOS Big Sur or later. Find out which macOS your Mac is using.
Select your backup disk in the Finder.
Choose File > Get Info from the menu bar. In the Info window that opens, look for the item labeled Format.
If the format isn't APFS, but you want improved Time Machine performance, use Disk Utility to erase the backup disk using the APFS format. This permanently deletes any backups and other data on that disk.
Set up Time Machine to use the backup disk again. After the first backup, future backups should be faster than before.