I changed MACs recently and my Time Machine back-ups of my actual documents has not happened although I've reconnected my hard drive

Time machine is an amazing work. It keeps the equivalent of every file that ever existed on your Mac and yet only copies an incremental backup when it runs.

It does this by creating a database of actual files, supplemented by links to files that already exist in your backup SET. It only looks to back up stuff in a Folder when MacOS data structure, the File System Event Store, indicates that Folder has recently changed.

use Time machine's "view other backups" feature, -OR- "inherit" that backup as your backup.

Browse Other Backup Disks

But there is a somewhat hidden way to access the timeline just for a specific disk, and that’s by holding down the Option key on your keyboard and clicking on the circle-clock icon in your menu bar.

from:

https://www.techjunkie.com/browse-other-backup-disks-time-machine/

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Time Machine - "Inherit Backup History" -… - Apple Community

what SHOULD have happened (if you are still using the same drive), is that you should have been offered to chance to "inherit the existing backup History' if you chose NOT to do that, your backup History begins anew.